Dissertations / Theses: 'Solar cells – Materials'

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Søiland, Anne Karin. "Silicon for Solar Cells." Doctoral thesis, Norwegian University of Science and Technology, Department of Materials Technology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-565.

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This thesis work consists of two parts, each with a different motivation. Part II is the main part and was partly conducted in industry, at ScanWafer ASA’s plant no.2 in Glomfjord.

The large growth in the Photo Voltaic industry necessitates a dedicated feedstock for this industry, a socalled Solar Grade (SoG) feedstock, since the currently used feedstock rejects from the electronic industry can not cover the demand. Part I of this work was motivated by this urge for a SoG- feedstock. It was a cooperation with the Sintef Materials and Chemistry group, where the aim was to study the kinetics of the removal reactions for dissolved carbon and boron in a silicon melt by oxidative gas treatment. The main focus was on carbon, since boron may be removed by other means. A plasma arc was employed in combination with inductive heating. The project was, however, closed after only two experiments. The main observations from these two experiments were a significant boron removal, and the formation of a silica layer on the melt surface when the oxygen content in the gas was increased from 2 to 4 vol%. This silica layer inhibited further reactions.

Multi-crystalline (mc) silicon produced by directional solidification constitutes a large part of the solar cell market today. Other techniques are emerging/developing and to keep its position in the market it is important to stay competitive. Therefore increasing the knowledge on the material produced is necessary. Gaining knowledge also on phenomenas occurring during the crystallisation process can give a better process control.

Part II of this work was motivated by the industry reporting high inclusion contents in certain areas of the material. The aim of the work was to increase the knowledge of inclusion formation in this system. The experimental work was divided into three different parts;

1) Inclusion study

2) Extraction of melt samples during crystallisation, these were to be analysed for carbon- and nitrogen. Giving thus information of the contents in the liquid phase during soldification.

3) Fourier Transform Infrared Spectroscopy (FTIR)-measurements of the substitutional carbon contents in wafers taken from similar height positions as the melt samples. Giving thus information of the dissolved carbon content in the solid phase.

The inclusion study showed that the large inclusions found in this material are β-SiC and β-Si3N4. They appear in particularly high quantities in the top-cuts. The nitrides grow into larger networks, while the carbide particles tend to grow on the nitrides. The latter seem to act as nucleating centers for carbide precipitation. The main part of inclusions in the topcuts lie in the size range from 100- 1000 µm in diameter when measured by the Coulter laser diffraction method.

A method for sampling of the melt during crystallisation under reduced pressure was developed, giving thus the possibility of indicating the bulk concentration in the melt of carbon and nitrogen. The initial carbon concentration was measured to ~30 and 40 ppm mass when recycled material was employed in the charge and ~ 20 ppm mass when no recycled material was added. Since the melt temperature at this initial stage is ~1500 °C these carbon levels are below the solubility limit. The carbon profiles increase with increasing fraction solidified. For two profiles there is a tendency of decreasing contents at high fraction solidified.

For nitrogen the initial contents were 10, 12 and 44 ppm mass. The nitrogen contents tend to decrease with increasing fraction solidified. The surface temperature also decreases with increasing fraction solidified. Indicating that the melt is saturated with nitrogen already at the initial stage. The proposed mechanism of formation is by dissolution of coating particles, giving a saturated melt, where β-Si3N4 precipitates when cooling. Supporting this mechanism are the findings of smaller nitride particles at low fraction solidified, that the precipitated phase are β-particles, and the decreasing nitrogen contents with increasing fraction solidified.

The carbon profile for the solid phase goes through a maximum value appearing at a fraction solidified from 0.4 to 0.7. The profiles flatten out after the peak and attains a value of ~ 8 ppma. This drop in carbon content is associated with a precipitation of silicon carbide. It is suggested that the precipitation of silicon carbide occurs after a build-up of carbon in the solute boundary layer.

FTIR-measurements for substitutional carbon and interstitial oxygen were initiated at the institute as a part of the work. A round robin test was conducted, with the Energy Research Centre of the Netherlands (ECN) and the University of Milano-Bicocci (UniMiB) as the participants. The measurements were controlled against Secondary Ion Mass Spectrometer analyses. For oxygen the results showed a good correspondence between the FTIR-measurements and the SIMS. For carbon the SIMS-measurements were significantly lower than the FTIR-measurements. This is probably due to the low resistivity of the samples (~1 Ω cm), giving free carrier absorption and an overestimation of the carbon content.

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Musselman, Kevin Philip Duncan. "Nanostructured solar cells." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609003.

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Velusamy, Tamilselvan. "Quantum confined materials for solar cells." Thesis, Ulster University, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.694653.

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The main objective of this thesis work is to synthesis quantum-confined structures, tailor their properties and investigate their applicability to photovoltaics. In this context, quantum-confined silicon nanocrystals (SiNes) are synthesized and surface engineered to tailor and understand their properties. Also a synthesis method for copper (Cu) oxide nanomaterials is developed with control over band energy diagram and optical properties. Finally these engineered quantum-confined nanostructures are successfully implemented in all-inorganic third generation photovoltaic devices with various device architectures. One of the important finding of this work is the dopant-dependant surface chemistry of doped SiNes and found that their optoelectronic properties and Fermi level are influenced by the different surface chemistries of the SiNCs. Secondly, the functionality of tailored SiNCs and Cu-oxide nanomaterials is demonstrated by fabricating all-inorganic solar cells. Some of these devices result in the highest open circuit voltage all-inorganic solar cells devices based on SiNCs. Devices that utilize SiNCs and CuO NPs were therefore presented for the first time in all-inorganic third generation architectures, which also made used of highly novel atmospheric pressure plasma processes.

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Cattley, Christopher Andrew. "Quaternary nanocrystal solar cells." Thesis, University of Oxford, 2016. http://ora.ox.ac.uk/objects/uuid:977e0f75-e597-4c7a-8f72-6a26031f8f0b.

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This thesis studies quaternary chalcogenide nanocrystals and their photovoltaic applications. A temperature-dependent phase change between two distinct crystallographic phases of stoichiometric Cu₂ZnSnS₄ is investigated through the development of a one pot synthesis method. Characterisation of the Cu₂ZnSnS₄ nanocrystals was performed using absorption spectroscopy, transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). An investigation was conducted into the effects of using hexamethyldisilathiane (a volatile sulphur precursor) in the nucleation of small (<7nm), mono-dispersed and solution-stable quaternary Cu₂ZnSnS₄ nanocrystals. A strategy to synthesize high quality thermodynamically stable kesterite Cu₂ZnSnS₄ nanocrystals is established, which subsequently enabled the systematic study of Cu₂ZnSnS₄ nanocrystal formation mechanisms, using optical characterization, XRD, TEM and Raman spectroscopy. Further studies employed scanning transmission electron microscopy (STEM) energy dispersive x-ray (EDX) mapping to examine the elemental spatial distributions of Cu₂ZnSnS₄ nanocrystals, in order to analyse their compositional uniformity. In addition, the stability of nanocrystals synthesised using alternative ligands is investigated using Fourier transform infrared spectroscopy, without solution based ligand substitution protocol is used to replace aliphatic reaction ligands with short, aromatic pyridine ligands in order to further improve Cu₂ZnSnS₄ colloid stability. A layer-by-layer spin coating method is developed to fabricate a semiconductor heterojunction, using CdS as an n-type window, which is utilised to investigate the photovoltaic properties of Cu₂ZnSnS₄ nanocrystals. Finally, three novel passivation techniques are investigated, in order to optimise the optoelectronic properties of the solar cells to the point where a power conversion efficiency (PCE) of 1.00±0.04% is achieved. Although seemingly modest when compared to the performance of leading devices (PCE>12%) this represents one of the highest obtained for a Cu₂ZnSnS₄ nanocrystal solar cell, fabricated completely under ambient conditions at low temperatures.

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Moore, Jennifer Rose. "New materials for solution-processible solar cells." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609301.

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Wang, Hongda. "Porphyrin-based materials for organic solar cells." HKBU Institutional Repository, 2015. https://repository.hkbu.edu.hk/etd_oa/200.

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A series of novel porphyrin materials with pushpull framework were designed and synthesized for organic solar cells (OSCs). To start with, a brief overview on the background of OSC, including dye-sensitized solar cells (DSSCs) and bulk heterojunction (BHJ) solar cells, and the porphyrin based materials for OSC applications was presented in Chapter 1. In Chapter 2, an efficient panchromatic light harvesting was demonstrated by the co-adsorption of a porphyrin molecule HD18 or HD19 and N719 in dye-sensitized solar cells. It is apparent that the porphyrin sensitizers show strong absorption in the Soret (400500 nm) and Q bands (600700 nm), while N719 shows efficient spectral response in the 500600 nm (between the Soret and Q bands), and the combination of these two kinds of dye molecules might display strong spectral response in the full-colour region. Mechanistic investigations were carried out by various spectral and electrochemical characterizations. The best co-sensitized device based on HD18 + N719 shows considerably enhanced power conversion efficiency of 8.27%, while those individually sensitized by HD18 and N719 display efficiencies of 6.74% and 6.90%, respectively. Subsequently, an optimized co-sensitized device based on the porphyrin HD18 and organic dye PT-C6 was fabricated by a stepwise adsorption of HD18 and PT-C6. The best performance of JSC/mA cm-2 =19.61, VOC/V = 0.74, FF = 0.69 and η = 10.1%, is superior to that of the individual device made from either HD18 (η = 7.4%) or PT-C6 (η = 8.2%) under the same conditions of fabrication. The post-adsorption of PT-C6 on the porphyrin-sensitized TiO2 anode surface not only enhances the spectral response of solar cells, but also greatly retards the back reaction between conduction-band electrons in TiO2 and the oxidized species ( I_3^-) in the electrolyte. In Chapter 3, a series of new donor-π-acceptor (DπA) porphyrin sensitizers with extended π-conjugation units were designed and synthesized for DSSC applications. Appending a phenothiazine (PTZ) donor moiety to the well-investigated porphyrin core and a variety of acceptors with electron deficient property at the opposite side can significantly red shift the absorption spectra to 700 nm in dyes (24). These different acceptor groups exert a significant influence on the electrochemical and photovoltaic properties of these sensitizers. These dyes have been evaluated in dye-sensitized solar cells, showing efficiencies of 0.90~7.29% with I^-/I_3^- based electrolytes. A detailed investigation on their physical, photophysical and electrochemical properties provided some important information on the factors affecting the main photovoltaic parameters. In Chapter 4, we designed and synthesized another series of dyes based on the rigid 2-aryl-1H-imidazo[4,5-b]porphyrin donors, in which an electron-accepting group was incorporated at the position 2 of imidazo unit via an aromatic spacer. Their photophysical and electrochemical properties, theoretical calculations and dye-sensitized solar cell performances have been investigated. The spectroelectrochemical data suggests the 1H imidazo unit can extend the conjugation length and lower the optical gap. As expected, the π conjugated substituents in all these dyes produced panchromatic absorption spectra over a wide range of wavelengths and IPCE spectra featuring a broad plateau in the region 430650 nm. In addition, both DFT computational and electrochemical data indicate a smaller HOMOLUMO energy gap for HD31Zn than that for dye 1, suggesting that a slightly more facile conjugation between the porphyrin core and the diketopyrrolopyrrole (DPP) unit through the 1H imidazo unit in HD31. Both Dye 1 and HD31Zn exhibited strong solvation effect in different solvents. The effects of solvents and their structures on the photophysical and photochemical properties and device performance have been studied in detail. The results indicate that porphyrin fused heterocycle as an effective electron donor and a suitable spacer between the donor and the acceptor can reduce the molecular aggregation through solvation effects. In Chapter 5, a series of conjugated DπA small molecules (YJ1YJ6, YJ13YJ15 and YJ16YJ19) for bulk heterojunction solar cells (BHJSCs) were prepared by the Sonogashira cross coupling of the electron rich porphyrin units with electron deficient benzothiadiazole (BT), DPP, or 3-ethylrhodanine moieties. The peripheral side chains on the porphyrin units like alkoxyl phenyl, alkyl, and (triisopropylsilyl)ethynyl (TIPS) can alter the solubility, conformation, and electronic properties of the obtained DπA small molecules, allowing the tuning of their photovoltaic properties when blended with fullerene derivatives. The presence of these side chains groups on porphyrin donor units affects the torsion angles between the side chains and the conjugated main chain, but resulting in only slightly different energy levels for the highest occupied molecular orbital (HOMO) for these molecules. Their performance in solution-processed solar cells is under studying. In Chapter 6, we reported the synthesis, electrochemical properties, and optical properties of seven novel BODIPY based π-conjugated materials. These dyes were synthesized via the Stille coupling reactions between the BODIPY units and electron donating groups (EDGs), such as 4,8-bis(5-(2-ethylhexyl)thiophen-2- yl)benzo[1,2-b:4,5-b′]dithiophene (BDT), 9,9-dioctyl-9H-fluorene (FL) or thieno[3,2-b]thiophene (TH). These donors were rationally chosen based on their gas phase ionization potential (IP) values estimated by density functional theory (DFT) calculations. Cyclic voltammetry of these dyes in dichloromethane solutions reveals that HOMOs of the resulting dyes correlated well with the ionization potentials (donor strength) of the donors. On the contrary, the lowest unoccupied molecular orbital (LUMO) energy levels of all dyes are fairly invariant, independent of the donors used. This suggests that the BODIPY moiety provides the primary influence on the LUMO levels of the materials. Two series of YJ9YJ11 and YJ21YJ23 show strong visible absorption in the red region. In addition, we presented the first example of a donor-acceptor BODIPY- containing conjugated copolymers, HDP6 and HDP7, with absorption over the entire spectrum of visible light and part of near infrared region (300900nm) making them suitable as additive for light-harvesting antenna. These dyes provide us with a toolset to tune the frontier molecular orbital energy levels, while retaining the low band gap and broad absorption of these dyes. Overall, these BODIPY molecules exhibited appropriate lower lying LUMO levels (3.70 ~ 3.86 eV) when compared with that of the P3HT, indicating their potential as acceptors for many donor materials in BHJSCs.

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Wang, Yiwen. "Stability of nonfullerene organic solar cells." HKBU Institutional Repository, 2019. https://repository.hkbu.edu.hk/etd_oa/666.

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The development of nonfullerene organic solar cells (OSCs) has attracted increasing interests because of the intrinsic advantages of nonfullerene acceptors, including their high absorption capability over the long wavelength region, tunable electronic properties, and excellent miscibility with polymer donors. Recently, power conversion efficiency (PCE) of >15 % for single-junction nonfullerene OSCs has been reported. Apart from the rapid progresses made in the cell efficiency, significant improvement in the stability of nonfullerene OSCs is required if the organic photovoltaic technology is to become a viable option for commercialization. The lifetime of OSCs is closely related to the intrinsic properties of the functional photoactive materials, e.g., the acceptors with suitable energy levels, morphology of bulk heterojunction (BHJ), formation of the active layer, interlayer engineering and device configuration. However, the comprehensive study of the impacts of the morphological properties and vertical phase separation in a BHJ on charge transport, built-in potential, charge recombination processes, PCE as well as the lifetime of nonfullerene OSCs has not been reported yet. This work has been focused on unraveling the stability of highly efficient OSCs using different nonfullerene acceptor/polymer blend systems, e.g., 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis (4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC): poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th), ITIC:poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl) -benzo[1,2-b:4,5- b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4', 5'-c'] dithiophene-4,8-dione)] (PBDB-T), and 3,9-bis(2-methylene-((3-(1,1 -dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene(IT-4F):poly[(2,6-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione)] (PBDB-T-2F). The lifetime of the nonfullerene OSCs has been analyzed systematically using a combination of morphology, photoelectron spectroscopy, light intensity-dependent current density-voltage measurements, transient photocurrent and aging studies. The effects of built-in potential (V0), charge extraction, and bimolecular recombination processes on the performance and stability of nonfullerene OSCs with regular and reverse configurations were studied. The results reveal that PTB7-Th:ITIC based OSCs with a reverse configuration are more favorable for efficient operation, due to the advantages of: (1) enhancement of charge collection by avoiding the holes passing through acceptor-rich region, which would otherwise occur in an OSC with a regular configuration, and (2) suppression of bimolecular recombination enabled by a higher V0. It shows that the PTB7-Th:ITIC based OSCs with a reverse configuration possess a slow degradation process, and >29% increase in PCE (8%) as compared to that of an optimized control OSC (6.1%). We found that a gradual decrease in V0 and hence the performance deterioration in the regular configuration PBDB-T:ITIC OSCs are caused mainly by the interfacial reaction between nonfullerene acceptor (ITIC) and poly(3,4-ethylenedioxythiophene) -poly(styrenesulfonate) (PEDOT:PSS) hole transporting layer (HTL). The reduction in V0, due to the unavoidable interfacial reaction between ITIC and PEDOT:PSS at the BHJ/HTL interface in the OSCs, can be overcome through interfacial engineering, , e.g., introducing a thin molybdenum oxide (MoO3) passivation layer. The effect of the HTL on stability of PBDB-T:IT-4F based OSCs has been analyzed using different HTLs, e.g., a pristine PEDOT:PSS layer, a MoO3-doped PEDOT:PSS layer and a pure MoO3 layer. It shows that MoO3-induced oxidation doping of PEDOT:PSS favors the stable and efficient operation of nonfullerene OSCs. The results suggest that a stable and high V0 across the BHJ is a prerequisite for attaining high efficiency nonfullerene OSCs with long-term stability.

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Li, Xuanhua, and 李炫华. "Plasmonic-enhanced organic solar cells." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/197526.

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Organic solar cells (OSCs) have recently attracted considerable research interest. However, there is a mismatch between their optical absorption length and charge transport scale. Attempts to optimize both the optical and electrical properties of the photoactive layer of OSCs have inevitably resulted in demands for rationally designed device architecture. Plasmonic nanostructures have recently been introduced into solar cells to achieve highly efficient light harvesting. The remaining challenge is to improve OSC performance using plasmonic nanotechnology, a challenge taken up by the research reported in this thesis. I systematically investigated two types of plasmonic effect: localized plasmonic resonances (LPRs) and surface plasmonic resonances (SPRs). Broadband plasmonic absorption is obviously highly desirable when the LPR effect is adopted in OSCs. Unfortunately, typical nanomaterials possess only a single resonant absorption peak, which inevitably limits the power conversion efficiency (PCE) enhancement to a narrow spectral range. To address this issue, I combined Ag nanomaterials of different shapes, including nanoparticles and nanoprisms. The incorporation of these mixed nanomaterials into the active layer resulted in wide band absorption improvement. My results suggest a new approach to achieving greater overall enhancement through an improvement in broadband absorption. I also explored the SPR effect induced by a metal patterned electrode with two parts. Most reports to date on back reflector realization involve complicated and costly techniques. In this research, however, I adopted a polydimethylsiloxane (PDMS)-nanoimprinted method to produce patterned back electrodes in OSCs directly, which is a very simple and efficient technique for realizing high-performance OSCs in industrial processes. Besides, a remaining challenge is that plasmonic effects are strongly sensitive to light polarization, which limits plasmonic applications in practice. To address this issue, I designed three-dimensional patterns as the back electrode of inverted OSCs, which simultaneously achieved highly efficient and polarization-independent plasmonic OSCs. In addition to investigating the two types of plasmonic effect individually, I also investigated their integrated function by introducing both LPRs and SPRs in one device structure. With the aim of achieving high-performance OSCs, I first demonstrated experimentally a dual metal nanostructure composed of Au nanoparticles (i.e. LPRs) embedded in the active layer and an Ag nanograting electrode (i.e. SPRs) as the back reflectors in inverted OSCs, which can generate a very strong electric field, in a single junction to improve the light absorption of solar cells. As a result, the PCE of the OSC reached 9.1%, making it one of the best-performing OSCs reported to date. In addition, as an important extension, I subsequently achieved tremendous near-field enhancement owing to multiple couplings, including nanoparticle-nanoparticle (LPR-LPR) couplings and nanoparticle-film (LPR-SPR) couplings, by designing a novel nanoparticle-film coupling system through the introduction of ultrathin monolayer graphene as a well-defined sub-nanogap between the Ag nanoparticles and Ag film. The graphene sub-nanogap is the thinnest nanogap (in atomic scale terms) to date, and thus constitutes a promising light-trapping strategy for improving future OSC performance.
published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy

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Li, Dai-Yin. "Texturization of multicrystalline silicon solar cells." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/64615.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 103-111).
A significant efficiency gain for crystalline silicon solar cells can be achieved by surface texturization. This research was directed at developing a low-cost, high-throughput and reliable texturing method that can create a honeycomb texture. Two distinct approaches for surface texturization were studied. The first approach was photo-defined etching. For this approach, the research focus was to take advantage of Vall6ra's technique published in 1999, which demonstrated a high-contrast surface texture on p-type silicon created by photo-suppressed etching. Further theoretical consideration, however, led to a conclusion that diffusion of bromine in the electrolyte impacts the resolution achievable with Vallera's technique. Also, diffusion of photocarriers may impose an additional limitation on the resolution. The second approach studied was based on soft lithography. For this approach, a texturization process sequence that created a honeycomb texture with 20 ptm spacing on polished wafers at low cost and high throughput was developed. Novel techniques were incorporated in the process sequence, including surface wettability patterning by microfluidic lithography and selective condensation based on Raoult's law. Microfluidic lithography was used to create a wettability pattern from a 100A oxide layer, and selective condensation based on Raoult's law was used to reliably increase the thickness of the glycerol/water liquid film entrained on hydrophilic oxide islands approximately from 0.2 pm to 2.5 pm . However, there remain several areas that require further development to make the process sequence truly successful, especially when applied to multicrystalline wafers.
by Dai-Yin Li.
Ph.D.

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Almeataq, Mohammed. "Development of new materials for solar cells application." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/4863/.

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Alfifi, Solyman Yahya. "Development of new materials for solar cells application." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/11443/.

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Heffernan, Shane. "Nanostructured CU₂O solar cells." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709220.

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Wei, Rongsheng. "Modelling of perovskite solar cells." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/119218/1/Rongsheng_Wei_Thesis.pdf.

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This project focuses on simulation performance of perovskite solar cells using two models. One is a simplified model developed for perovskite absorber layer of PSCs by using matlab program to investigate the effect of density of state, relative dielectric permittivity and band gap energy of the perovskite material on the device performance. The other model is based on SCAPS to investigate the influence of hole mobility and band gap offset of different hole transport materials on device performance.

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Saif, Addin Burhan K. (Burhan Khalid). "The challenges of organic polymer solar cells." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/62740.

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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 108-110).
The technical and commercial prospects of polymer solar cells were evaluated. Polymer solar cells are an attractive approach to fabricate and deploy roll-to-roll processed solar cells that are reasonably efficient (total PV system efficiency>10%), scalable and inexpensive to make and install (<100 $/m2). At a cost of less than 1$/Wp, PV systems will be able to generate electricity in most geographical locations at costs competitive to coal's electricity (at 5-6 cents/KWh) and will make electricity available to more people around the world (-20% of the world population is without electricity). In this chapter, we explore organic polymer solar cell technology. The first chapter discusses the potential impact of solar cells on electricity markets and the developing world and its promise as a sustainable scalable low carbon energy technology. The second chapter discusses some of the complexity in designing polymer solar cells from new materials and the physics involved in some detail. I also discuss the need to develop new solution processed transparent conductors, cost effective encapsulation and long life flexible substrates. The third chapter discusses polymer solar cells cost estimates and how innovative designs for new modules could reduce installation costs. In the final chapter I discussed the prospects for commercialization of polymer solar cells in several niche markets and in grid electricity markets; the commiseration prospects are dim especially with the uncertainty in the potential improvement in polymer solar cell stability.
by Burhan K. Saif Addin.
M.Eng.

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Griffitts, Fletcher G. "Fullerenes in Solar Energy Cells." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/honors/394.

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This project involves controlling and characterizing the morphology of the active layer in a special type of organic photovoltaics (OPVs), consisting of porphyrin-fullerene composites, with emphasis on electron exchange interactions between the two components. The Vienna Ab Initio Simulation Package (VASP) is applied to model a variety of donor-acceptor complexes containing fullerene and porphyrin in terms of their stabilities as well as their geometric, electronic, and charge transfer features. The goal is to identify supramolecular chain structures with highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) that may serve as electron (hole) transfer channels in a photovoltaic device. A stable structure, involving the planar adsorption of a porphyrin unit on a C60 hexagon, has been identified. The results for fullerene have been extended to phthalocyanine–fullerene dyads where the fullerene-derived unit Phenyl-C61-butyric acid methyl ester (PCBM) is connected to a porphyrin analogous electron donor through two oxygen-linked benzene rings. In both cases, the HOMO is located on the porphyrin segment, the LUMO on the fullerene component. As a fullerene, PCBM is a material of very high electron affinity, but it has better solubility properties than fullerene. It is often used in plastic solar cells or flexible electronics in conjunction with electron donor materials such as P3HT or other polymers. The results of our work contribute to the ongoing effort of using computational modeling to identify fullerene-based materials of potential relevance for organic photovoltaics.

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Moh, Lionel C. H. (Lionel Chuan Hui). "Enhancing materials for fuel cells and organic solar cells through molecular design." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111251.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
In an effort to make alternative energy competitive to fossil fuels, research in improving efficiencies of solar cells and fuel cells have grown rapidly over the last few decades. One prominent strategy to improving the efficiencies in these devices focuses on engineering materials with customized molecular structure for enhancements in specific properties. Herein, new organic materials are designed and synthesized to enhance selected properties for applications in fuel cells and solar cells. In chapter 1, triptycene poly(aryl ethers) are synthesized and characterized for enhancing ion conductivity of ion exchange membranes in fuel cells. Triptycene motif is incorporated to increase charge density and fractional free volume in the membranes. In Chapter 1.2, sulfonated triptycene poly(ether ether ketone) (S-tripPEEK) is synthesized and studied for proton exchange membranes (PEM). Increasing fractional free volume in the membrane results in high water uptake at relative humidity (RH) from 10 %RH to 90 %RH and higher proton mobility in the membranes. S-tripPEEK membranes show proton conductivities of 334 mS/cm at 85 °C at 90 %RH and 0.37 mS/cm at 85 °C at 20 %RH as compared to 18.9 mS/cm and 0.0014 mS/cm observed in commercially available Nafion117[superscript TM] membranes. In Chapter 1.3, methylimidazolium triptycene poly(ether sulfone)s (MeIm-tripPES) are made for alkaline anion exchange membranes (AAEM) and are found to have ion conductivities of 104 mS/cm at 80 °C in water. Controlled nanophase separation with increased domain size contributed by the triptycene moiety lead to the high observed conductivities. However, the methylimidazolium functional groups on the membranes are not stable to alkaline conditions in the operation of a fuel cell. In Chapter 2, dithiolodithiole (C₄S₄) heterocycle was synthesized and studied as a new building block for organic photovoltaic materials. As an electron-rich fused-ring motif, C₄S₄ is expected to be a more effective electron donor. Comparison with analogous thiophene derivatives shows that C4S4 moiety raises the highest occupied molecular orbital (HOMO) by 0.7 - 1.0 eV, suggesting a stronger electron donating character than thiophene. Furthermore, crystal structures of C4S4 molecules show planarity in the molecule which further reduces the bandgap.
by Lionel C. H. Moh.
Ph. D.

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17

Karlsson, Martin. "Materials Development for Solid-State Dye-Sensitized Solar Cells." Doctoral thesis, Uppsala universitet, Fysikalisk kemi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-165458.

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The dye-sensitized solar cell (DSC) is a photovoltaic technology with the potential to efficiently and economically harvest and convert energy from the sun to electrical power. DSCs are built using abundant and low cost materials such as titanium dioxide (TiO2) and organic dye molecules. The dye molecule acts as a light absorber funneling electrons from its photo-excited state to the TiO2. A redox mediator which typical consists of iodide/tri-iodide undergoes redox reactions at the counter electrode and the oxidized dye molecule creating a circuit between the two. Solid-state versions of the DSC are also being investigated. In these devices the liquid electrolyte is exchanged with solid hole transporting material in order to both simplify the solar cell production as well as increasing the open-circuit potential and stability of the solar cell. One main draw-back, which limits the increase in conversion efficiency of solid-state DSC is the faster electron recombination dynamics between electrons in the TiO2 and holes in the solid hole transporter. Currently the highest performing liquid electrolyte DSC reaches a conversion efficiency of over 12 %, while the solid-state DSC is tailing with 7 %. Materials development is crucial for further development of the DSC technology, hopefully leading to better stability and higher efficiency. Many types of dye molecules, redox mediators as well as hole transporting materials and working electrode materials have all been tested and modified in the past in order to improve DSC performance. Significant further improvement of DSC technology requires a better understanding of the operating principle behind the DSC and the interaction between the different components. This requires advanced characterization methods for materials and solar cells. In this thesis, new materials for DSC have been developed, tested and characterized using advanced methods. Atomic layer deposition was employed to develop a new working electrodes based on the core-shell SnO2-TiO2 material. These working electrodes were successfully used in both liquid and solid-state DSC to decrease the electron recombination dynamics and increase conversion efficiencies. The molecular structure of sensitizing dyes also plays a major role in electron recombination. Thus, investigating different molecular structures of sensitizing dyes is of importance when trying to improve DSC performance. Seven new molecular dye structures based on three different chromophore units were investigated in both liquid electrolyte and solid-state DSC. For example, adding a second anchoring group on the D35 molecular structure improved the light harvesting capabilities of the dye but did not result in DSC devices with higher conversion efficiency. Increasing the bulkiness of the molecular dye structure facing away from the TiO2 surface yielded on the other hand higher both slower electron recombination and higher conversion efficiencies. The effects of oxygen on solid-state DSC using spiro-OMeTAD were also studied. The chemical oxidation of the solid-state hole transporting material was found to depend on both time and storing conditions of the complete DSC devices. Solar cells with higher conversion efficiency were found for solid-state DSC stored under ambient air conditions before measured. Finally, a novel and efficient organic tandem solar cell was demonstrated built using a solid-state DSC and a bulk heterojunction solar. The 6 % efficient tandem cell almost perfectly added the photo-potentials of the subcells together while keeping the photo-current intact.

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Yang, Lei. "Hole Transport Materials for Solid-State Mesoscopic Solar Cells." Doctoral thesis, Uppsala universitet, Fysikalisk kemi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-232271.

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The solid-state mesoscopic solar cells (sMSCs) have been developed as a promising alternative technology to the conventional photovoltaics. However, the device performance suffers from the low hole-mobilities and the incomplete pore filling of the hole transport materials (HTMs) into the mesoporous electrodes. A variety of HTMs and different preparation methods have been studied to overcome these limitations. There are two types of sMSCs included in this doctoral thesis, namely solid-state dye-sensitized solar cells (sDSCs) and organometallic halide perovskite based solar cells. Two different types of HTMs, namely the small molecule organic HTM spiro-OMeTAD and the conjugated polymer HTM P3HT, were compared in sDSCs. The photo-induced absorption spectroscopy (PIA) spectra and spectroelectrochemical data suggested that the dye-dye hole conduction occurs in the absence of HTM and appears to be of significant importance to the contribution of hole transport. The PIA measurements and transient absorption spectroscopy (TAS) indicated that the oxidized dye was efficiently regenerated by a small molecule organic HTM TPAA due to its excellent pore filling. The conducting polymer P3HT was employed as a co-HTM to transfer the holes away from TPAA to prohibit the charge carrier recombination and to improve the hole transport. An alternative small molecule organic HTM, MeO-TPD, was found to outperform spiro-OMeTAD in sDSCs due to its more efficient pore filling and higher hole-mobility. Moreover, an initial light soaking treatment was observed to significantly improve the device performance due to a mechanism of Li+ ion migration towards the TiO2 surface. In order to overcome the infiltration difficulty of conducting polymer HTMs, a state-of-the-art method to perform in-situ photoelectrochemical polymerization (PEP) in an aqueous micellar solution of bis-EDOT monomer was developed as an environmental-friendly alternative pathway with scale-up potential for constructing efficient sDSCs with polymer HTMs. Three different types of HTMs, namely DEH, spiro-OMeTAD and P3HT, were used to investigate the influence of HTMs on the charge recombination in CH3NH3PbI3 perovskite based sMSCs. The photovoltage decay measurements indicate that the electron lifetime (τn) of these devices decreases by one order of magnitude in the sequence τspiro-OMeTAD > τP3HT > τDEH.

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Safdar, Amna. "Nano-structures and materials for wafer-scale solar cells." Thesis, University of York, 2018. http://etheses.whiterose.ac.uk/20561/.

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This thesis addresses two of the main materials for solar cells, namely silicon and the family of halide perovskites. For silicon, light trapping structures are investigated for solar cell applications while perovskite materials are investigated as a gain material for optoelectronic applications. Light trapping allows the capture of photons that might otherwise be lost, especially at the red end of the spectrum where silicon is less absorptive. The key is to enhance the efficiency of silicon cells by thinning down the wafer and reducing the bulk recombination losses and to achieve a higher Voc while maintaining strong light absorption (represented by a high short circuit current, Jsc) by applying efficient light trapping schemes. It is still an open question whether nanostructures are beneficial for real devices, especially since highly efficient solar cells employ >100 μm thick absorber materials and use wet etched micron-sized pyramids for light trapping. In this thesis, I conduct a study which compares nanostructures and pyramid microstructures on wafer-based silicon solar cells. This study is important because (1) most light trapping nanostructures are investigated only in the optical regime, while I realize them on silicon devices to analyze both their optical and their electrical character; (2) nanostructures perform better than microstructures in wafer based silicon solar cells, highlighting the effectivity of nanostructures even in wafer-based silicon. Here, the nanostructures comprise wet and dry-etched quasi-random structres and they are compared with pyramidal microstructures. A photocurrent as high as 38 mA/cm2 for a dry etched quasirandom nanostructure is attained experimentally, which is 3.2 mA/cm2 higher than wet etched pyramids fabricated in the same batch. The other material which is now becoming very popular in the solar cell community is the family of metal halide perovskite materials that are increasingly attracting the attention of optoelectronics researchers, both for solar cell and for light emission applications. The ultimate is in simplicity, however, is to observe lasing from a continuous thin film, which has not been aimed before. Here, I show perovskite random lasers; they are deposited at room temperature on unpatterned glass substrates and they exhibit a minimum threshold value of 10 μJ/cm2. A rather special feature is that some of the films exhibit single and dual mode lasing action, which is rarely observed in random lasers. This work fully exploits the simplicity of the solution-based process and thereby adds an important capability to the emerging field of perovskite-based light emitters.

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20

Fuentes, Pineda Rosinda. "Triphenylamine-based hole transport materials for perovskite solar cells." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31410.

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The rapid development in perovskite solar cells (PSC) has generated a tremendous interest in the photovoltaic community. The power conversion efficiency (PCE) of these devices has increased from 3.8% in 2009 to a recent certified efficiency of over 20% which is mainly the product of the remarkable properties of the perovskite absorber material. One of the most important advances occurred with the replacement of the liquid electrolyte with a solid state hole conductor which enhanced PCE values and improved the device stability. Spiro-OMeTAD (2,2',7,7'-tetrakis(N,N'-di-p-methoxyphenylamine)- 9,9'-spirobifluorene) is the most common hole transport material in perovskite solar cells. Nevertheless, the poor conductivity, low charge transport and expensive synthetic procedure and purification have limited its commercialisation. Triphenylamines (TPA) like Spiro-OMeTAD are commonly employed due to the easy oxidation of the nitrogen centre and good charge transport. Other triarylamines have similar properties to Spiro-OMeTAD but are easier to synthesise. The aim of this doctoral thesis is to investigate different types of hole transport materials in perovskite solar cells. Three different series of triphenylamine-based HTM were designed, synthesised, characterised and studied their function in perovskite solar cells. A series of five diacetylide-triphenylamine (DATPA) derivatives (Chapter 3) with different alkyl chain length in the para position was successfully synthesised through a five step synthesis procedure. A range of characterisation techniques was carried out on the molecules including; optical, electrochemical, thermal and computational methods. The results show that the new HTMs have desirable optical and electrochemical properties, with absorption in the UV, a reversible redox property and a suitable highest occupied molecular orbital (HOMO) energy level for hole transport. Perovskite solar cell device performances were studied and discussed in detail. This project studied the effect of varying the alkyl chain length on structurally similar triarylamine-based hole transport materials on their thermal, optical, electrochemical and charge transport properties as well as their molecular packing and solar cell parameters, thus providing insightful information on the design of hole transport materials in the future. The methoxy derivative showed the best semiconductive properties with the highest charge mobility, better interfacial charge transfer properties and highest PCE value (5.63%). The use of p-type semiconducting polymers are advantageous over small molecules because of their simple deposition, low cost and reproducibility. Styrenic triarylamines (Chapter 4) were prepared by the Hartwig-Buchwald coupling followed by their radical polymerization. All monomers and polymers were fully characterised through electrochemical, spectroscopic and computational techniques showing suitable HOMO energy levels and desirable optoelectrochemical properties. The properties and performance of these monomers and polymers as HTMs in perovskite solar cells were compared in terms of their structure. Despite the lower efficiencies, the polymers showed superior reproducibility on each of the device parameters in comparison with the monomers and spiro-OMeTAD. Finally, star-shaped structures combine the advantages of both small molecules, like well-defined structures and physical properties, and polymers such as good thermal stability. Two star-shaped triarylamine-based molecules (Chapter 5) were synthesised, fully characterised and their function as hole-transport materials in perovskite solar cells studied. These materials afford a PCE of 13.63% and high reproducibility and device stability. In total this work provided three series of triarylamine-based hole transport materials for perovskite solar cells application and enabled a comparison of the pros and cons of different design structures: small-molecule, polymeric and star-shaped.

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Müller, Toni. "Infrared Absorber Materials in Organic Small Molecule Solar Cells." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-178375.

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Broadening the spectrum available to solar cells towards infrared wavelengths is one way to increase efficiency of organic solar devices. This thesis explores the possibilities of these organic heterojunction devices and two different material classes in thin ﬁlms and organic solar devices: tin phthalocyanines (SnPcs) and aza-bodipys. To estimate the efficiency reachable under sunlight, model calculations are done for single and tandem cells. These calculations include a distinction between the optical gap and the electrical gap and the splitting of the quasi-Fermi levels. With a number of assumptions, e.g. a ﬁll factor (FF) and an external quantum efficiency (EQE) within the absorption range of 65%, the resulting efficiencies are 15% in a single cell and of 21% in a tandem cell. Halogenation is known to lower the energy levels of molecules without chang-ing the optical band gap. Three different ﬂuorinated and chlorinated SnPcs are investigated and compared to the neat SnPc. While chlorination of SnPc worsens the transport properties of the active layer leading to a lowered FF, the ﬂuorina-tion of SnPc results in the intended increase in VOC and, consequently, efficiency for planar heterojunctions. In bulk heterojunction, however, ﬂuorination does not change the efficiency probably due to the unstably bound ﬂuorine. One method to modify the ionization potential (IP) and the absorption of the second material class, the aza-bodipys, is the annulation of the benzene ring. The energy levels determined by CV and UPS measurement and DFT-calculation show very good agreement and can be linked to a decrease in VOC: The Ph4-bodipy (not benzannulated) device has an efficiency of 1.2% with an EQE reaching up to 800nm and a VOC of almost 1V. The Ph2-benz-bodipy device shows a Voc of 0.65V and an efficiency of 1.1%, the EQE reaching up to 860nm. The variation of the molecule’s end groups to vary their IP is successfully employed for three different benz-bodipys: The variation results in a decrease of the optical gap from 1.5eV for the phenyl group, to 1.4eV for the MeO group, and 1.3eV for the thiophene group with the effective gap and the VOC following this trend. Efficiencies of 1.1% and 0.6% in combination with C60 can be reached in mip-type devices. Ph2-benz-bodipy is then optimized into a single cell with an efficiency of 2.9%. In a tandem cell with DCV6T-Bu4:C60, a Voc of 1.7V, a FF of 57% and an efficiency of 5% is reached
Die Erweiterung des verfügbaren Spektrums in den Infrarotbereich ist eine Möglichkeit, die Effizienz organischer Solarzellen zu erhöhen. Diese Arbeit erkundet das Potential dieser Heteroübergänge und zwei Materialklassen in dünnen Schichten und Bauelementen: Zinnphthalozyanine (SnPc) und aza-Bodipys. Um die potentielle Effizienz abzuschäötzen, werden Modellberechnungen für Einzel- und Tandemzellen durchgeführt, unter Berücksichtigung des Unterschieds von optischer und elektrischer Bandlücke und der Quasiferminiveauaufspaltung. Mithilfe einiger Annahmen (z.B. Füllfaktor (FF) und externe Quanteneffizienz (EQE) gleich 65%) lässt sich die Einzelzelleffizienz auf 15%, die Tandemzellefﬁzienz auf 21% abschätzen. Halogenierung kann die Energieniveaus organischer Moleküle herabsetzen, ohne die optische Bandlücke zu verändern. Drei verschiedene chlorierte und ﬂuorierte SnPcs werden mit dem reinen SnPc verglichen. Während die Chlorierung die Transporteigenschaften der aktiven Schicht und den FF verschlechtern, erhöht die Fluorierung wie erwartet Leerlaufspannung (VOC) und Effizienz im ﬂachen Übergang, nicht jedoch in der Mischschicht, vermutlich aufgrund des nicht stabil gebundenen Fluors. Ein Weg, Ionisationspotential (IP) und Absorption der aza-Bodipy zu verändern, ist die Anelierung des Benzenrings. Die durch CV und UPS ermittelten und mittels DFT errechneten Energieniveaus stimmen gut überein und führen zu einer Verringerung der VOC: Die Zelle mit nichtaniliertem Ph4-bodipy zeigt eine Effizienz von 1.2%; das EQE reicht bis 800nm, die VOC beträgt fast 1V. Die Ph2-benz-bodipy-Zelle zeigt eine VOC von 0.65V und eine Effizienz von 1.1%, das EQE reicht bis 860nm. Der Austausch der Endgruppen zur Vergrößerung des IP, erfolgreich angewandt auf drei Benz-Bodipy-Verbindungen, führt zu einer Verringerung der optischen Bandlücke: von 1.5eV (Phenyl) über 1.4eV (MeO) zu 1.3eV (Thiophen); effektive Bandlücke und Voc folgen diesem Trend. Effizienzen von 1.1% und 0.6% in Kombination mit C60 werden in mip-Zellen erreicht. Ph2-benz-bodipy zeigt in einer optimierten nip-Zelle sogar eine Effizienz von 2.9%. Eine Tandemzelle mit DCV6T-Bu4:C60 zeigt eine Voc von 1.7V, einen FF von 57% und eine Effizienz von 5%

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22

Shao, Qinghui. "Optimized designs and materials for nanostructure based solar cells." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://proquest.umi.com/pqdweb?index=0&did=1957340961&SrchMode=2&sid=2&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1268668089&clientId=48051.

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Thesis (Ph. D.)--University of California, Riverside, 2009.
Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 12, 2010). Includes bibliographical references. Also issued in print.

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23

Massip, Sylvain. "Electronic and morphological studies on materials for organic solar cells." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609785.

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An, Tao M. Eng Massachusetts Institute of Technology. "Evaluation of concentration solar cells for terrestrial applications." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45356.

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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.
Includes bibliographical references (leaves 43-44).
Solar energy has become a hot prospect for the future replacement of fossil fuels, which have limited reserves and cause environmental problems. Solar cell is such a device to directly generate electricity from this clean and renewable energy source. Today's photovoltaic market is dominated by Si flat-plate solar modules, but its production cost is still much higher than that of fossil-fuelled power plant. To reduce this cost, sunlight concentrator, which is made of cheap materials like glass, polymers and metals, can be used together with the solar cell. It is able to focus a wide column of sunrays onto a small piece of solar cell, thus the required dimension of the cell is greatly reduced. The cost analysis showed that it is preferable to use high-end solar cells with higher concentration ratio, since this leads to great increase in output power and less significant increment in overall cost, as this cell cost is small compared with the entire solar unit cost. The best concentration system with most efficient solar cell is found to be able to achieve a lower average price than Si flat-plates, and with sufficient market penetration, its average cost may even be comparable to that of a newly established coal-fired power plant. Therefore, concentration solar module has great potential to secure its share in the fast-growing photovoltaic market, serving as supplement to currently dominating fossil fuels and even replacement for them. Existing IP was also carefully reviewed to find out possible aspects for future developments. Finally, possible business strategies were studied and discussed. It was recommended to start as an IP company, which may expand to manufacturing company in the long run.
by Tao An.
M.Eng.

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Tan, Kwan Wee. "Commercialization potential of dye-sensitized mesoscopic solar cells." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/54206.

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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 67-73).
The price of oil has continued to rise, from a high of US$100 per barrel at the beginning 2008 to a new record of above US$140 in the recent weeks (of July). Coupled with increasing insidious greenhouse gas emissions, the need to harness abundant and renewable energy sources is never more urgent than now. The sun is the champion of all energy sources and photovoltaic cell production is currently the world's fastest growing energy market. Dye-sensitized solar cells (DSCs) are photoelectrochemical cells which mimic the natural photosynthesis process to generate solar electricity. Typically, a monolayer of dye sensitizer molecules is anchored onto a semiconductor mesoporous film such as TiO₂ to generate charges on exposure to illumination. The nanocrystalline particulate threedimensional network provides high surface area coverage for the photogeneration process and percolation of charges. In the thesis, we will review the current research efforts to optimize the DSC performance and develop probable applications to complement existing solid-state photovoltaic technologies. We believe the large and rapidly expanding solar market offers a prime commercial opportunity to deliver a DSC product for mass adoption by consumers. DSC is kept at a low production cost because it bypasses conventional vacuum-based semiconductor processing technologies, instead relying on solution and chemical processing routes. However, our cost modeling analysis show the TCO glass substrate and ruthenium dyes could constitute more than 90% of the overall materials cost.
(cont.) Thus, we recommend new technological approaches must be taken to keep the substrate pricing low and continuously improve the energy conversion efficiencies to further lower the production cost.
by Kwan Wee Tan.
M.Eng.

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26

Brivio, Federico. "Atomistic modelling of perovskite solar cells." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.698992.

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This thesis focuses on the study of hybrid perovskites properties for the purposes of photovoltaic applications. During the almost four years PhD project that has lead to this thesis the record photovoltaic efficiency for this technology has in- creased from 10.9% to 22.1%. Such a significant pace of development can be com- pared with few other materials. It is for this reason that hybrid perovsites have at- tracted impressive research efforts. We approached the study of such unique ma- terials using computational ab-initio techniques, and in particular Density Func- tional Theory. We considered different materials, but most of the attention was concentrated on MAPI (CH 3 NH 3 PbI 3 ). The results are divided in three chapters, each exploring a different material prop- erty. The first chapter reports the electronic structure of the material bulk, sur- faces, and other electronic-related properties such as the rotation barrier for the organic component and the Berry phase polarization. The second chapter focuses on the vibrational properties primary employing the harmonic approximation but also extends to the quasi-harmonic approximation. The outcome of these calculations permitted us to calculate theoretical IR and Ra- man spectra which are in good agreement with different experimental measure- ments. The quasi-harmonic approximation was used to calculate temperature dependent properties, such as the Grüneisen parameter, the thermal dependence of heat capacity and the thermal volumetric expansion. The third and last chapter reviews the thermodynamic properties of binary halide compounds. The cobination of ab-initio calculations with the generalised quasi- chemical approximation has allowed to study the stability of mixed composition perovskites. The results certified a set of stable structures that could stand at the base of observed phenomena of photo-degradation of hybrid perovskite based devices. All three chapters have been written to understand the chemical and physical behaviour of hybrid perovskites and to extended and contribute to the under- standing of experimental work.

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Cheung, Kai-yin, and 張啓賢. "Metallopolyyne polymers based bulk heterojunction (BHJ) solar cells." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42841719.

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Xie, Fengxian, and 解凤贤. "Novel inorganic material and film formation process for high performance organic solar cells." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/199892.

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Organic solar cell (OSC) is a highly promising research field with a strong potential to realize low cost solar cells with flexibility and light weight. Although OSC power conversion efficiency (PCE) exceeding 9% has been achieved recently, great efforts are still needed to strive a PCE over 10% making OSC ready for commercialization. Besides the demand of high PCE, other considerations, such as easy solution process, stability and large area processing, are also required for mass production in future. With the understanding of key technical issues that still challenge OSC towards widely spread applications, our worksarefocusingon1) applying the solution processed inorganic materials to ameliorate the intrinsic drawback in OSCs; and 2)proposing novel and simple solution process to improve electrical properties of OSCs by controlling the film quality thus the electrical properties during the film formation process. Detailed work is listed below: 1. Incorporating of metal nanoparticles (NPs) for improving OSC efficiency Metal NPs are selected as the candidate for improving OSC efficiency through their unique optical and electrical properties. Our results show that (1a) When meal NPs are incorporated in the hole transport layer (HTL) poly-(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the PCE of OSCs are improved due to enhanced conductivity and rough surface. (1b) When metal NPs are embedded in the active layer, OSC performance can be further enhanced due to improvement in light absorption and electrical properties. When we incorporate Au NPs in all organic layers of OSCs, accumulation improvements in OSC performances can be achieved. (1c) When metal NPs are incorporated in electron transport layer of TiO2, the experimental results show that the enhanced charge extraction under solar illumination can be attributing to the UV-excited electrons transfer from TiO2electron transport layer and storage by Au NPs. 2. Solution processed metal oxide thin film for high efficient hole transporting layer (HTL) The solution-processed transition metal oxides (TMOs) have attracted great attention due to their superior air-stability properties and universal energy level alignment with organic materials. In this thesis, we propose a one-step method to synthesize low-temperature solution-processed TMOs such as molybdenum oxide and vanadium oxide, with good film quality, desirable electrical properties, and improved device stability, for HTLs applications. 3. Self-assemble metal oxide for high efficient electron transporting layer (ETL) We propose a self-assemble and solution-processed method in fabricating ETLs composed of TiO2 NPs that can simultaneously achieve good film uniformity and homogeneity, and electron transport properties. We believe this new method will be capable for large-area applications in future. 4. Vertical morphology control for active layer. Besides carrier transport layers, the morphology of the active layer will significantly affect its electrical and optical properties and thus device performance. We propose up-side-down method to modify the nano-morphology blend along vertical direction, which is beneficial to vertical charge transport and thus producing higher OSC performances. The film-growth dynamics of polymer blends is studied, which has been neglected in most study of OSC morphology by others.
published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy

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Peters, Stefan. "Rapid thermal processing of crystalline silicon materials and solar cells /." Allensbach : UFO Atelier für Gestaltung und Verlag, 2004. http://www.loc.gov/catdir/toc/fy0805/2007493330.html.

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Gresser, Roland. "Azadipyrromethenes as near-infrared absorber materials for organic solar cells." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-78871.

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Organic solar cells have the potential to become a low-cost photovoltaic technology. One approach to further increase the device efficiency aimsvto cover the near-infrared region of the sunvspectrum. However, suitable absorber materials are rare. This thesis focuses on the material class of aza-bodipy and dibenzo-aza-bodipy as near-infrared absorber materials for organic solar cells. Besides the synthesis of novel thiophene-substituted aza-bodipys, azadiisoindomethenes were prepared by the addition of Grignard reagents to phthalodinitrile an subsequent reduction with formamide. Starting from these azadiisoindomethenes as precursors, complexes with borondifluoride, boroncatechole and transition metals were synthesized. The optical and electrochemical properties of all compounds prepared were investigated by experimental and theoretical methods. The (dibenzo-)aza-bodipys are characterized by their electronic structure, comprising a central electron acceptor core and peripheral electron donor units. The substituents at the donor units offer a stronger impact on the HOMO energy than on the LUMO energy. Electron donating substituents at the donor units result in an overall decreased HOMO-LUMO gap. This allows to redshift the absorption maximum up to 800 nm. The corresponding dibenzo-analogues already demonstrate a bathochromic shift of the absorption compared to the (non-annulated) aza-bodipys. Yet, the central acceptor is weakened and a further redshift by substituents is less distinct. The compounds can be thermally evaporated in high vacuum. The required thermal stability is increased in some cases by boroncatechol compared to borondifluoride complexes, without significant influence on the optical and electrochemical properties. Besides the characterization of the molecular properties, promising materials were evaluated in thin fifilms and solar cell devices. The charge carrier mobility in the measured compounds were found to be between 10E-6 and 10E-4 cm2V-1s-1. The charge transport parameters were calculated on the basis of obtained single crystal structures. It was found that a high charge carrier mobility may be attributed to a better molecular overlap and a short intermolecular distance in the corresponding solid state structure. Selected materials were characterized in organic solar cells. In solution processed devices, the dibenzo-aza-bodipys reached efficiencies of 1.6 % and 2.1 %, as donor materials in combination with PC61BM and PC71BM as acceptor. The main limiting factor in these devices turned out to be the low fill factor of 30 %. From a series of vacuum processed devices with aza-bodipys and dibenzo-aza-bodipys, increased voltages were obtained with decreasing HOMO energy of the bodipy derivatives. A suitable near-infrared absorbing dibenzo-aza-bodipy exhibited a contribution to the photocurrent from 750 - 950 nm
Die organische Photovoltaik hat das Potential eine kostengünstige Solarzellentechnologie zu werden. Ein Ansatz die Effizienz weiter zu steigern besteht darin den aktiven Spektralbereich in den nahen Infrarotbereich zu erweitern. Bisher gibt es jedoch nur wenige geeignete Materialien. In dieser Arbeit werden Verbindungen aus der Materialklasse der Aza-Bodipy und Dibenzo-Aza-Bodipy als Absorbermaterialien für den nahen Infrarotbereich zur Verwendung in organischen Solarzellen untersucht. Neben der Synthese von neuen Thiophen-substituierten Aza-Bodipys wurden Azadiisoindomethine durch die Addition von Grignardverbindungen an Phthalodinitril und anschließender Reduktion mit Formamid dargestellt. Ausgehend von den Azadiisoindomethinen sind neue Bordifluorid, Borbrenzcatechin und Übergangsmetallkomplexe synthetisiert worden. Alle Substanzen sind mit experimentellen und theoretischen Methoden auf ihre optischen und elektrochemischen Eigenschaften hin untersucht worden. Die elektronische Struktur der (Dibenzo-)Aza-Bodipys ist charakterisiert durch periphere Elektronendonoreinheiten um einen zentralen Elektronenakzeptor. Die langwelligste Absorptionsbande kann in beiden Systemen durch Elektronen schiebende Gruppen an den Donoreinheiten bathochrom, auf über 800 nm verschoben werden. Die Ursache liegt in einem stärkeren Einfluss der Substituenten auf das HOMO als auf das LUMO und einem damit einhergehenden stärkeren Anstieg der HOMO-Energie woraus eine verkleinerte HOMO-LUMO Lücke resultiert. Die Dibenzo-Aza-Bodipys zeichnen sich durch eine rotverschobene Absorption gegenüber den (nicht benzannulierten) Aza-Bodipys aus. Jedoch ist der Akzeptor in den Dibenzo-Aza-Bodipys abgeschwächt, so dass die Rotverschiebung durch die selben Substituenten weniger stark ausgeprägt ist und die Energieniveaus tendenziell höher liegen. Die Verbindungen lassen sich thermisch im Vakuum verdampfen. Die für das Verdampfen wichtige thermische Stabilität, kann durch Austausch von Bordifluorid mit Borbrenzcatechol erhöht werden, ohne die optischen und elektronischen Eigenschaften wesentlich zu beeinflussen. Neben der Charakterisierung der molekularen Eigenschaften, sind einige Verbindungen im Dünnfifilm auf ihre elektrischen Eigenschaften und in Solarzellen untersucht worden. Die Ladungsträgerbeweglichkeit liegt bei den gemessenen Verbindungen zwischen 10E-6 und 10E-4 cm2V-1s-1. Durch Berechnung der Ladungstransportparameter auf Basis erhaltener Kristallstrukturen ist eine höhere Beweglichkeit auf eine günstigere Packung und einen geringeren intermolekularen Abstand zurückgeführt worden. Ausgewählte Verbindungen sind als Donormaterialien in organischen Solarzellen charakterisiert worden. Aus Lösungsmittel prozessierte Solarzellen mit Dibenzo-Aza-Bodipys erreichen eine Effifizienz von 1.6 % mit PC61BM, und 2.1 % mit PC71BM als Akzeptor. Der Effizienz limitierende Faktor ist hierbei der niedrige Füllfaktor von ca. 30 %. In vakuumprozessierten Solarzellen mit planarem Dono-Akzeptor-Übergang von Aza-Bodipys und Dibenzo-Aza-Bodipys hat sich gezeigt, dass die erhaltene Spannung mit abnehmender HOMO Energie der Materialien gesteigert wird. Ein geeignetes Dibenzo-Aza-Bodipy Material ist mit einen Beitrag zum Photostrom im nahen Infrarotbereich, von 750 - 950 nm, gezeigt worden

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31

Sortland, Øyvind Sunde. "Wet Chemical Synthesis of Materials for Intermediate Band Solar Cells." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16327.

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The economical feasibility of commercial, single-junction solar cells is limited by high costs and limited efficiencies. New solar cell concepts and materials are sought to decrease the production costs and increase the efficiency. Intermediate band solar cells (IBSCs) show a promising concept for increased efficiency up to 46.77% as they employ three band gaps that can be matched to the solar spectrum to minimize fundamental losses. Doping of copper gallium disulphide (CuGaS2) with transition metals like Fe and Ni to high concentrations can theoretically form an intermediate band (IB), which for Fe doping gives nearly optimal band gaps for IBSC applications. Copper gallium disulphide is synthesized in an environmentally friendly, inexpensive and simple hydrothermal synthesis which may contribute to decreased costs of solar cell production.The hydrothermal synthesis is developed to produce copper gallium disulphide from copper(I) chloride (CuCl), gallium(III) chloride (GaCl3) and excess thiourea (Tu) (SC(NH2)2) in deionized water. The influence of varying synthesis parameters on product purity, yield and morphology has been investigated through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDS) is used to investigate doping of copper gallium disulphide and identify particle morphologies formed by different phases. Formation of copper gallium disulphide proceeds through slow decomposition of Tu, driven by an equilibrium shift due to hydrogen disulphide (H2S) evolution and precipitation of sulphides like the intermediate phase digenite (Cu2-δS) into which Ga3+ ions are incorporated. An additional impurity of copper(II) sulphide (CuS) is commonly formed, and gallium(III) hydroxyoxide (GaO(OH)) forms at pH > 0.5. Products of high purity and yield are obtained at 250 °C with concentrations above 0.060 M copper(I) chloride and gallium(III) chloride with the complexing agent 1-pentanethiol, and 0.319 M without 1-pentanethiol. Introducing nickel(II) chloride (NiCl2) or iron(III) chloride (FeCl3) in the hydrothermal synthesis forms vaesite (NiS2) or iron pyrite (FeS2) impurities, respectively, and copper gallium disulphide is not doped to a desirable concentration for IB formation.Color variations in the products reveal off-stoichiometries which contribute to a wide range of particle and crystallite morphologies within each product. Yellow, stoichiometric copper gallium disulphide particles have been deposited on a Si(100) substrate and growth of a red, Ga-rich film was achieved with 1-pentanethiol. These products were subject to photoluminescence spectroscopy (PL) along with off-stoichiometric powders of doped and undoped products, but no luminescence was obtained, possibly due to high defect densities and non-radiative recombination. Dispersions of powders were also subject to absorption spectroscopy which indicate extensive scattering due to wide ranges of particle sizes. The morphology of powder products shows particularly large variations within and between the products. Nanoplate and pyramidal crystallites are produced through nucleation and growth to form network structures and polycrystalline spheres, rods and rose-like particles, which along with the crystallites have varying irregularities and sizes.

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32

Liu, Jiewei. "Investigating low cost hole transporting materials for perovskite solar cells." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:51073048-faed-439d-9ce5-cbe4c55fe4b2.

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Organic-inorganic halide perovskites (CH3NH3PbI3) have attracted strong attention of photovoltaic research community since 2012, benefiting from the low cost of organolmetal halide perovskite precursors and their simple solution processability. However, the chemical instability of this material, especially in high humidity environment, restricts its photovoltaic application in industry. This thesis is focusing on employing novel hole transporting materials (HTMs) for perovskite solar cells (PSCs). Besides their main responsibility acting as a hole selective layer increasing the photovoltaic performance, HTMs can also play an additional role serving as moisture blocking layers, enhancing the stability of PSCs. Chapter 2 presents the general background knowledge of the physics of solar cells, delving deeper into the working principle of PSCs and related researches about the HTMs and stability of the devices. In chapter 3, the device fabrication techniques and the characterization methods used are presented in details. Commencing from chapter 4, the application of two kinds of HTMs and related studies are discussed. Chapter 4 demonstrates the use of a p-type organic material, PEDOT, on 'regular' structured PSCs, achieving devices with decent power conversion efficiency (PCE) but relatively huge hysteresis and low stabilized power output (SPO). Stability analysis shows this organic material provides a better protection of the perovskite film comparing to that of doped Spiro-OMeTAD, which is the most generally used HTM. Chapter 5 presents a study about CuSCN, an inorganic p-type semiconductor, being applied in PSCs as HTM. The CuSCN based devices show comparable performance to that of Spiro-OMeTAD based devices, but an interfacial degradation mechanism is found to facilitate the perovskite degradation even in inert atmosphere. A facile sealing protocol is established to deal with this problem, leading to super stable photovoltaic devices under thermal stressing. The following chapter 6 demonstrates a CuI doping technique to improve the hole transporting effectiveness of CuSCN layer. This doping technique modifies the morphology of CuSCN film and leads to a substantial improvement in the photovoltaic performance.

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33

Körner, Christian. "Oligothiophene Materials for Organic Solar Cells - Photophysics and Device Properties." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-121509.

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The rapidly increasing power conversion efficiencies (PCEs) of organic solar cells (OSCs) above 10% were made possible by concerted international research activities in the last few years, aiming to understand the processes that lead to the generation of free charge carriers following photon absorption. Despite these efforts, many details are still unknown, especially how these processes can be improved already at the drawing board of molecular design. To unveil this information, dicyanovinyl end-capped oligothiophene derivatives (DCVnTs) are used as a model system in this thesis, allowing to investigate the impact of small structural changes on the molecular properties and the final solar cells. On thin films of a methylated DCV4T derivative, the influence of the measurement temperature on the charge carrier generation process is investigated. The observed temperature activation in photoinduced absorption (PIA) measurements is attributed to an increased charge carrier mobility, increasing the distance between the charges at the donor/acceptor (D/A) interface and, thus, facilitating their final dissociation. The correlation between the activation energy and the mobility is confirmed using a DCV6T derivative with lower mobility , exhibiting a higher activation energy for charge carrier generation. Another parameter to influence the charge carrier generation process is the molecular structure. Here, alkyl side chains with varying length are introduced and their influence on the intramolecular energy levels as well as the absorption and emission properties in pristine and blend films with the acceptor C60 are examined. The observed differences in intermolecular order (higher order for shorter side chains) and phase separation in blend layers (larger phase separation for shorter side chains) are confirmed in PIA measurements upon comparing the temperature dependence of the triplet exciton lifetimes. A proposed correlation between the side chain length and the coupling between D and A, which is crucial for efficient charge transfer, is not confirmed. The presented flat heterojunction solar cells underline this conclusion, giving similar photocurrent densities for all compounds. Differences in PCE are related to shifts of the energy levels and the morphology of the blend layer in bulk heterojunction devices. Furthermore, the impact of the electric field on the charge carrier generation yield is investigated in a proof-of-principle study, introducing PIA measurements in transmission geometry realized using semitransparent solar cells. The recombination analysis of the photogenerated charge carriers reveals two recombination components. Trapped charge carriers or bound charge pairs at the D/A interface are proposed as an explanation for this result. The miscibility of D and A, which can be influenced by heating the substrate during layer deposition, is of crucial importance to obtain high PCEs. In this work, the unusual negative influence of the substrate temperature on DCV4T:C60 blend layers in solar cells is investigated. By using optical measurements and structure determination tools, a rearrangement of the DCV4T crystallites is found to be responsible for the reduced absorption and, therefore, photocurrent at higher substrate temperature. The proposed blend morphology at a substrate temperature of 90° C is characterized by a nearly complete demixing of the D and A phases. This investigation is of particular relevance, because it shows the microscopic origins of a behavior that is contrary to the increase of the PCE upon substrate heating usually reported in literature. Finally, the optimization steps to achieve a record PCE of 7.7% using a DCV5T derivative as donor material are presented, including the optimization of the substrate temperature, the active layer thickness, and the transport layers
Der rasante Anstieg des Wirkungsgrads von organischen Solarzellen über die Marke von 10% war nur durch länderübergreifende Forschungsaktivitäten während der letzten Jahre möglich. Trotz der gemeinsamen Anstrengungen, die Prozesse, die zwischen der Absorption der Photonen und der Ladungsträgererzeugung liegen, genauer zu verstehen, sind einige Fragen jedoch immer noch ungelöst, z.B. wie diese Prozesse schon auf dem Reißbrett durch die gezielte Änderung bestimmter Molekülstrukturen optimiert werden können. Um dieses Ziel zu erreichen, werden in dieser Arbeit Dicyanovinyl-substituierte Oligothiophene (DCVnTs) verwendet. Diese Materialien bieten die Möglichkeit, kleine strukturelle Änderungen vorzunehmen, deren Einfluss auf die molekularen und auf die Solarzelleneigenschaften untersucht werden soll. Der Einfluss der Messtemperatur auf den Prozess der Ladungsträgertrennung wird hier an einer methylierten DCV4T-Verbindung in einer dünnen Schicht untersucht. Die bei photoinduzierter Absorptionsspektroskopie (PIA) beobachtete Aktivierung dieses Prozesses mit zunehmender Temperatur wird auf eine erhöhte Ladungsträgerbeweglichkeit zurückgeführt. Der dadurch erhöhte effektive Abstand der Ladungen an der Grenzfläche zwischen Donator (D) und Akzeptor (A) erleichtert die endgültige Trennung der Ladungsträger. Durch den Vergleich mit einer DCV6T-Verbindung wird der Zusammenhang zwischen der Aktivierungsenergie und der Beweglichkeit bekräftigt. Die kleinere Beweglichkeit äußert sich dabei in einer größeren Aktivierungsenergie. Darüber hinaus kann der Ladungsträgergenerationsprozess auch von der Molekülstruktur abhängen. In dieser Arbeit wird untersucht, wie sich die Länge von Alkylseitenketten auf die Energieniveaus der Moleküle, aber auch auf die Absorptions- und Lumineszenzeigenschaften der Materialien in reinen und in Mischschichten mit dem Akzeptor C60 äußert. Die ermittelten Unterschiede bezüglich der Molekülordnung (geordneter für kürzere Seitenketten) und der Phasengrößen in Mischschichten (größere Phasen bei kürzerer Kettenlänge) werden in der Untersuchung der Temperaturabhängigkeit der Lebensdauer von Triplettexzitonen mittels PIA-Messungen bestätigt. Für Solarzellen ist von Bedeutung, ob sich die Seitenkettenlänge auf die Wechselwirkung zwischen D und A auswirkt. Der vermutete Zusammenhang wird hier nicht bestätigt. Ein ähnlicher Photostrom für alle untersuchten Verbindungen in Solarzellen mit planaren Heteroübergängen unterstreicht diese Schlussfolgerung. Unterschiede im Wirkungsgrad werden auf Änderungen der Energieniveaus und die Morphologie in Mischschichtsolarzellen zurückgeführt. Des Weiteren wird in einer Machbarkeitsstudie der Einfluss des elektrischen Felds auf die Generationsausbeute freier Ladungsträger untersucht. Dafür werden halbtransparente Solarzellen verwendet, die es ermöglichen, PIA-Messungen in Transmissionsgeometrie durchzuführen. Als mögliche Erklärung für das Auftreten zweier Rekombinationskomponenten in der Analyse des Rekombinationsverhaltens der durch Licht erzeugten Ladungsträger werden eingefangene Ladungsträger und gebundene Ladungsträgerpaare an der D/A-Grenzfläche genannt. Das Mischverhalten von D und A kann durch ein Heizen des Substrates während des Verdampfungsprozesses eingestellt werden, was von entscheidender Bedeutung für eine weitere Steigerung des Wirkungsgrades ist. Für DCV4T:C60-Mischschichtsolarzellen wird jedoch eine Verschlechterung des Wirkungsgrads zu höheren Substrattemperaturen beobachtet. Durch optische Messungen und Methoden zur Schichtstrukturbestimmung wird dieser Effekt auf eine Umordnung der DCV4T-Kristallite für hohe Substrattemperaturen und die damit verbundene Verringerung der Absorption und damit auch des Photostroms zurückgeführt. Bei einer Substrattemperatur von 90° C sind die D- und A-Komponenten fast vollständig entmischt. Dieses Beispiel ist von besonderer Bedeutung, weil hier die Ursachen für ein Verhalten aufgezeigt werden, das entgegen den Beispielen aus der Literatur eine Abnahme des Wirkungsgrads beim Aufdampfen der aktiven Schicht auf ein geheiztes Substrat zeigt. Schließlich werden die Optimierungsschritte dargelegt, mit denen Solarzellen mit einer DCV5T-Verbindung als Donatormaterial auf einen Rekordwirkungsgrad von 7,7% gebracht werden. Dabei wird die Substrattemperatur, die Dicke der aktiven Schicht und die Transportschichten angepasst

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34

Mapel, Jonathan King. "The application of photosynthetic materials and architectures to solar cells." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35302.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 51-60).
Photosynthetic approaches to redesigning photovoltaics (PV) offer an attractive route towards achieving high-efficiency, low-cost solar energy transduction. This thesis explores two routes toward this end: the direct integration of photosynthetic structures into solid-state devices and the architectural redesign of organic solar cells to more closely parallel photosynthesis. The highly accent photosynthetic reaction center is the site of exciton dissociation in photosynthesis, analogous to the role of the donor-acceptor interface in organic PV. This thesis describes the successful integration of reaction centers with organic semiconductors into solid-state devices. Although functional, we nd that these devices suer the same limitation as the more traditional organic PV: the ability to absorb enough light. Photosynthetic bacteria and plants compartmentalize the processes leading to light energy conversion. This spatial separation of structures augments the evolutionary design space: the processes of photon absorption and exciton dissociation occur in two separate locations, allowing the independent functional optimization of each.
(cont.) Applying a similar approach to PV would similarly remove the need for multifunctional materials, bypassing limiting tradeos and permitting the utilization of new material systems. To this end, I propose a novel architecture and present initial conclusions on theoretical performance eciency. Fabricated devices demonstrate the system is viable and suggests that further improvements in device design will enable highly ecient photovoltaics.
by Jonathan King Mapel.
S.M.

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35

Lobez, Comeras Jose Miguel. "New functional polymers for sensors, smart materials and solar cells." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/73367.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2012.
Vita. Cataloged from PDF version of thesis.
Includes bibliographical references.
Organic polymers can be used as the active component of sensors, smart materials, chemical-delivery systems and the active layer of solar cells. The rational design and modification of the chemical structure of polymers has enabled control over their properties and morphology, leading to the advancement of nanotechnology. A deeper understanding of structure-property relationships, as described in this thesis, affords control over the nanostructure of devices made from these macromolecular materials, which is crucial to the optimization of their performance. In Chapter 1, a new sensor for ionizing radiation based on composites of electron beam lithography resists, poly (olefin sulfone)s (POSs), and multiwalled carbon nanotubes is presented. The polymeric active component is radiation labile and its degradation after a sensing event leads to morphological and electrical changes in the composite at the nanoscale. As a result, a signal can be detected. Systematic sensitivity improvements can be accomplished by rational modifications of the chemical structure of the polymer side-chains. Orthogonal postpolymerization modifications performed using "click" chemistry, incorporate functional groups capable of increasing either the homogeneity of the composite, or its opacity towards radiation. In Chapter 2, a smart hybrid polymer composed of a POS and a silicone linked by "click" chemistry is described. By tuning the chemical structure of these two components and varying their ratio, composites with different mechanical properties and hardness can be achieved. This elastomeric smart material exhibits switchable mechanical properties: exposure to mild bases triggers disassembly into its monomers and individual constituents. In Chapter 3, the design, synthesis and properties of new polymer surfactant additives for photovoltaic devices is shown. The AB alternating regioregular polythiophene copolymer additives are obtained via a combinatorial approach, and contain functional groups in every other repeat unit. In Chapter 4 incorporation of small amounts of these polymer additives (0.25 weight %) is shown to result in large increases of up to 30% in the power conversion efficiency of organic solar cells consisting primarily of the benchmark system of poly (3-hexylthiophene) and Phenyl-C6 1-butyric acid methyl ester (PCBM) as the active layer. This effect is mainly due to the presence of dipoles at the interface of the bulk heterojunction introduced by the additives, which prevent charge recombination and lead to increases in the photocurrent collected across the polymer-fullerene interface. In Chapter 5, the synthesis of liquid crystalline polymer brushes is described, and their supramolecular and self-assembly properties are studied. The solid-state ordering and alignment properties of these highly substituted polymers can be affected by chemically tuning their mesogenic oligomeric side-chains, the length of the polymer backbone and the degree of crosslinking. The morphologies obtained with these macromolecules are interesting from the point of view of future photovoltaic applications.
by Jose Miguel Lobez Comeras.
Ph.D.

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36

Kraner, Stefan. "Improved organic materials and electronic properties of organic solar cells." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-190237.

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Organic photovoltaic (OPV) is a promising technology for renewable energy at low cost. Over the last five years, the power conversion efficiency (PCE) has doubled to 12%, which still is clearly lower than commercially available inorganic solar cells with a PCE around 20%. One approach to improve the PCE is to complement the conversion of light into electrical energy with the infrared (IR) part of the solar spectrum. However, the fundamental difference between organic and inorganic semiconductors is the exciton binding energy. Compared to inorganic semiconductors, in organic materials the exciton binding energy is more than 20 times higher, leading to strongly bound electron hole pairs, which are primarily generated upon photo-excitation. To dissociate these charges, in OPV, a donor-acceptor system is used. However, the energetics of this donor-acceptor system lowers the obtained open circuit voltage, representing one major loss of OPV as compared to inorganic solar cells. In the first part of this work, three benzannulated 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (aza-BODIPY) infrared absorbing donor dyes with methyl, methoxy, or without side-group attached are investigated. The solar cells with the highest PCE, i.e. the devices using the donor molecule without a side-group, exhibit a difference between the optical and the effective gap of 0.17 eV. It reflects the "driving force" for the electron to transfer from the donor to the acceptor, and is lowest for the best performing device, indicating that in the devices used efficient charge dissociation does not require large electron transfer energy loss. A - for OPV - relatively high open circuit voltage of 0.81 V is measured and when compared to the optical gap of the donor, a voltage loss of 0.74 V is obtained, reflecting the high voltage losses in OPV. In inorganic devices these voltage loss is around 0.4 V. One approach to lower this difference in the voltage loss is to lower the exciton binding energy of neat organic materials, leading to a larger exciton size. A saturation of the exciton size at about 1.2 nm is calculated by time dependent density functional method (TD-DFT) for one dimensional conjugated organic molecules with a size larger than 4nm. For the largest size of the exciton, provided by the poly(benzimidazobenzophenanthroline) (BBL), a Coulomb interaction of 0.4 eV between the electron and hole wave function is calculated, leading to an estimated exciton binding energy of about 0.2 eV, serving as a lower limit for the organic molecules investigated. The exciton binding energy can further be lowered by increasing the dielectric constant or by introducing a charge transfer (CT) state between two adjacent molecules. It is shown for the ladder polymer BBL that the dielectric function, including ionic and electronic contributions, can be calculated by a new method within the DFT and TD-DFT framework. In agreement with ellipsometry measurements, a highly anisotropic dielectric constant is obtained, which is 8.3 along the backbone of the polymer and around 3 perpendicular to the polymer. The high dielectric constant along the backbone originates from the strong delocalization of the electrons along the π-system. The ionic contribution increases the mean value of the dielectric constant from 3.6 to 4.2. In order to further increase the dielectric constant, different polar side-chains are attached to the ladder polymer BBL and their dielectric constant is calculated. A strong increase of the dielectric constant to about 17 is obtained by attaching a zwitterionic side-chain to the BBL monomer. In order to lower the exciton binding energy by a CT state, a charge transfer from a donor to an acceptor molecule must be introduced. The Coulomb binding energy of intermolecular CT states are calculated. It is shown that an intermolecular CT state of two π-stacked BBL oligomers does not exhibit a lower Coulomb binding energy as compared to the intramolecular binding energy. However, by a spatial separation of the donor and the acceptor molecule, in-line of the polymer backbone, the Coulomb binding energy is reduced from 0.40 eV to 0.24 eV. Combining such CT states with the high dielectric constant obtained by zwitterionic side-chains would lead to an exciton binding energy close to the thermal energy, resulting in spontaneous free carrier generation on neat materials. This could potentially reduce the voltage losses and increase the PCE in OPV devices significantly
Die organische Photovoltaik stellt eine kostengünstige, erneuerbare und daher zukunftsgerichtete Energieversorgung dar. Die Umwandlungseffizienz organischer Solarzellen von Sonnenenergie in elektrische Energie konnte über die letzten fünf Jahre auf 12% verdoppelt werden. Kommerziell erhältliche anorganische Solarzellen weisen im Vergleich dazu eine Effizienz von ca. 20% auf. Eine Möglichkeit, die Effizienz organischer Solarzellen zu erhöhen, ist die Umwandlung von Licht in Elektrizität nicht nur im sichtbaren Bereich, sondern zusätzlich auch im infraroten Bereich des Sonnenspektrums. Der größte Unterschied zwischen den organischen und anorganischen Solarzellen liegt allerdings in der Exzitonbindungsenergie, welche in organischen Materialien ca. 20 Mal größer ist. Um das Exziton in freie Ladungsträger zu trennen, wird in organischen Solarzellen deshalb ein Donator-Akzeptor-Übergang benutzt, welcher unter anderem auch für den Spannungs- und damit für den Effizienzverlust von organischen Solarzellen verantwortlich ist. Im ersten Teil der Dissertation werden verschiedene funktionalisierte Donator-Moleküle, die infrarotes Licht absorbieren, untersucht. Die Donator-Moleküle ohne zusätzliche Funktionalisierungsgruppe weisen dabei die höchste Umwandlungseffizienz auf. In den besten Zellen kann ein Unterschied zwischen der optischen und effektiven \"Bandlücke\" von 0,17 eV gemessen werden. Dieser Unterschied stellt die treibende Kraft für den Übergang des Elektrons vom Donator zum Akzeptor dar. Da jedoch dieser Unterschied in der besten Solarzelle am geringsten ist, scheint die Dissoziation der Ladungsträger in den untersuchten Donator-Akzeptor-Systemem nicht vom ihm abzuhängen. Die gemessene relative hohe Leerlaufspannung von 0,81 V ist 0,74 V kleiner als die effektive Bandlücke und zeigt die hohen Spannungsverluste organischer Solarzellen. Die Spannungsverluste anorganischer Solarzellen liegen im Bereich von 0,4 V. Ein Ansatz, um die Spannungsverluste zu verkleinern, liegt in der Reduzierung der Exzitonbindungsenergie, woraus ein größeres Exziton erfolgt. Mit der zeitabhängigen Dichtefunktionaltheorie wird an einer Reihe organischer Moleküle gezeigt, dass die Exzitongröße bei einer Moleküllänge (oder Konjugationslänge) größer als 4nm bei 1,2nm sättigt. Für das größte Exziton, welches im Leiterpolymer Poly(benzimidazobenzophenanthroline) (BBL) vorhanden ist, wird eine Coulomb-Bindungsenergie von 0,4 eV berechnet und eine Exzitonbindungsenergie von 0,2 eV abgeschätzt. Die Exzitonbindungsenergie kann entweder durch Erhöhung der Dielektrizitätskonstante oder durch Erzeugung eines Ladungstransfer-Zustandes weiter verringert werden. Es wird gezeigt, dass mit einer neu entwickelten Methode auf Basis der Dichtefunktionaltheorie die ionischen und elektronischen Beiträge zur dielektrischen Funktion von BBL berechnet werden können. Die berechneten anisotropen Werte stimmen gut mit Werten aus Ellipsometriemessungen überein. Entlang der Polymerkette erhalten wir eine hohe Dielektrizitätskonstante von 8,3 und senkrecht dazu von ca. 3. Die hohe Dielektrizitätskonstante entlang der Polymerkette kann auf die starke Delokalisation der π-Elektronen zurückgeführt werden. Der Mittelwert der Dielektrizitätskonstante wird durch die ionischen Beiträge von 3,6 auf 4,2 erhöht. Um die Dielektrizitätskonstante weiter zu erhöhen, werden verschiedene polare Seitenketten am BBL-Polymer angebracht und die Dielektrizitätskonstante berechnet. Es wird gezeigt, dass die Anbringung einer zwitterionischen Seitenkette am BBL-Monomer die Dielektrizitätskonstante auf 17 erhöht. Um die Exzitonbindungsenergie durch einen Ladungstransfer-Zustand zu verringern, werden ein Donator- und ein Akzeptor-Molekül benötigt. Die Coulomb-Bindungsenergien der intermolekularen Ladungstransfer-Zustände werden berechnet. Es wird gezeigt, dass intermolekulare Ladungstransfer-Zustände zwischen zwei π-gestapelten BBL-Oligomeren keine Verringerung der Coulomb-Bindungsenergie bewirken. Bei einer räumlichen Trennung des Donator- und Akzeptor-Moleküls entlang der Polymerkette kann die Coulomb-Bindungsenergie von 0,40 eV auf 0,24 eV gesenkt werden. Eine Kombination aus diesem Ladungstransfer und der Erhöhung der Dielektirizitätskonstante durch zwitterionische Seitenketten kann zu einer niedrigen Exzitonbindungsenergie, nahe der thermischen Energie, und damit zu freien Ladungsträgern führen. Der damit verringerte Spannungsverlust kann die Umwandlungseffizienz organischer Solarzellen signifikant erhöhen

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37

Ebenhoch, Bernd. "Organic solar cells : novel materials, charge transport and plasmonic studies." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/7814.

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Organic solar cells have great potential for cost-effective and large area electricity production, but their applicability is limited by the relatively low efficiency. In this dissertation I report investigations of novel materials and the underlying principles of organic solar cells, carried out at the University of St Andrews between 2011 and 2015. Key results of this investigation: • The charge carrier mobility of organic semiconductors in the active layer of polymer solar cells has a rather small influence on the power conversion efficiency. Cooling solar cells of the polymer:fullerene blend PTB7:PC₇₁BM from room temperature to 77 K decreased the hole mobility by a factor of thousand but the device efficiency only halved. • Subphthalocyanine molecules, which are commonly used as electron donor materials in vacuum-deposited active layers of organic solar cells, can, by a slight structural modification, also be used as efficient electron acceptor materials in solution-deposited active layers. Additionally these acceptors offer, compared to standard fullerene acceptors,advantages of a stronger light absorption at the peak of the solar spectrum. • A low band-gap polymer donor material requires a careful selection of the acceptor material in order to achieve efficient charge separation and a maximum open circuit voltage. • Metal structures in nanometer-size can efficiently enhance the electric field and light absorption in organic semiconductors by plasmonic resonance. The fluorescence of a P3HT polymer film above silver nanowires, separated by PEDOT:PSS, increased by factor of two. This could be clearly assigned to an enhanced absorption as the radiative transition of P3HT was identical beside the nanowires. • The use of a processing additive in the casting solution for the active layer of organic solar cells of PTB7:PC₇₁BM strongly influences the morphology, which leads not only to an optimum of charge separation but also to optimal charge collection.

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38

Barrows, Alexander T. "Novel materials and deposition techniques for solution processed solar cells." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/12428/.

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Whilst many advances have been made in the field of solution processed solar cells (SPSCs), there is still much work to be done if they are to fulfil their potential and reduce the cost of commercial photovoltaic devices. This thesis aims to assist in moving towards this objective by investigating ways to overcome some of the barriers to the commercialization of SPSCs. Such barriers include the costly and mechanically brittle electrode material of indium tin oxide, the use of solution deposition techniques which are not compatible with large-scale production, and a lack of understanding of the properties of promising new semiconducting materials such as organometal halide perovskites. In this work a novel indium-free multilayer semi-transparent electrode has been fabricated and incorporated as the anode in polymer solar cells. Whilst molybdenum oxide is typically used as the ‘seed layer’ material in such trilayer structures, its replacement with tellurium dioxide has been found to lead to an enhanced transmittance in the optimised electrodes and to an increased short circuit current when such electrodes are employed in polymer solar cells. The roll-to-roll compatible deposition technique of ultrasonic spray-coating has, for the first time, been successfully used for the fabrication of films of the organometal trihalide perovskite CH3NH3PbI3-xClx. Such films were subsequently successfully employed as the active layer in planar solar cells. This deposition technique is then extended to hole transporting and electron transporting materials in order to move towards a fully spray-deposited solar cell. Finally, a combination of structural investigation techniques have been employed to monitor the formation of the perovskite CH3NH3PbI3-xClx during thermal annealing of a precursor film. In-situ X-ray scattering measurements are used together with ex-situ scanning electron microscopy in order to correlate the evolution of the film during annealing to solar cell performance. In addition, the activation energy for the transition from precursor to perovskite has been calculated.

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39

Shen, Zhangfeng. "Engineering Carbon-Semiconductor Hybrid Materials for Photocatalysis and Solar Cells." Thesis, Curtin University, 2017. http://hdl.handle.net/20.500.11937/66005.

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Carbon-semiconductor hybrid materials (CSHMs) are promising candidates for solar energy conversion because of their enhanced light harvesting ability and the prolonged charge carrier separation. In this thesis, a series of CSHMs has been successfully fabricated and applied in photocatalysis and dye-sensitized solar cells. The aim of this thesis is to develop cost-effective methods to prepare CSHMs with appropriate morphologies, compositions, and interfacial contact to promote the efficiency of photocatalysis and solar energy conversion.

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40

Cui, Chaohua. "Conjugated polymer and small-molecule donor materials for organic solar cells." HKBU Institutional Repository, 2014. https://repository.hkbu.edu.hk/etd_oa/37.

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This thesis is dedicated to developing conjugated polymer and small-molecule donor materials for solution-processable organic solar cells. To begin with, a brief introduction of organic solar cells (OSCs) and an overview of donor materials development were presented in Chapter 1. In chapter 2, we used carbon-carbon triple bands as linkage of the TVT unit to develop a new building block, ATVTA. Small molecules S-03, S-04, and S-05 with ATVTA as building block showed broad absorption spectra and low-lying HOMO energy levels. S-01 with TVT unit and S-02 with AT2 as building block were also synthesized for clear comparison. OSCs devices based on S-01 and S-02 showed a Voc of 0.88 V and 0.89 V, respectively. The device based on S-03 exhibited a high Voc of 0.96 V, leading to a PCE of 2.19%. The devices based on S-04 and S-05 afforded a notable Voc over 1.0 V. The results demonstrate that ATVTA unit is a promising building block for extending π conjugation of the molecules without pulling up their HOMO energy levels. Chapter 3 focused on the development of 2D-conjugated small-molecule donor materials. The 2D-conjugated small molecule S-06 possesses excellent solution processability, broad absorption feature, respectable hole mobility and good film-forming morphology. The conjugated thiophene side chain not only effectively extends the absorption spectrum, but also lowers the HOMO energy level, which is desirable for obtaining high Voc. The BHJ OSCs based on S-06:PC70BM (1:0.5, w/w) afforded a high PCE of 4.0% and a notable FF of 0.63 without any special treatment needed. This preliminary work demonstrates that this kind of 2D-conjugated small molecules offer a good strategy to design new photovoltaic small molecule-based donor materials with high FF and Voc for high-efficiency OSCs. The consistently developed two 2D-conjugated small molecules S-07 and S-08 also possess low-lying HOMO energy levels. OSC device based on S-07:PC60BM (1:3, w/w) afforded a notable Voc of 0.96 V, with a PCE of 2.52%. BHJ devices based on S-08 will be fabricated and tested to investigate its photovoltaic properties in the near future. We developed a series of oligothiophenes with platinum(Ⅱ) as the building block in Chapter 4. These small metallated conjugated small molecules exhibited broad spectra and relatively low-lying HOMO energy levels in the range of –5.27 eV to –5.40 eV. Introducing platinum(Ⅱ) arylene ethynylenes as building block can be considered as an approach to obtain small-molecule donors with satisfactory absorption features and HOMO energy levels. Nevertheless, due to the low FF, the PCEs of these donor materials based devices are lower than 2%. Fine tuning the film morphologies of this kind of metallated small-molecule donor materials should be carried out to improve their photovoltaic performance. We addressed an efficient approach to improve the photovoltaic properties by side chain engineering in 2D-conjugated polymers in Chapter 5. Considering the fact that the Voc of PBDTTT based devices is less than 0.8 V, we introduced alkylthio substituent on the conjugated thiophene side chains of the 2D-conjugated copolymer to further improve the photovoltaic performance of the 2D-conjugated copolymers PBDTTTs. The weak electron-donating ability of the alkylthio side chains effectively down-shifted the HOMO energy level of PBDTT-S-TT by 0.11 eV in comparison to the corresponding polymer with alkyl substitution on the conjugated thiophene side chains. The PSC device based on PBDTT-S-TT showed an enhanced Voc of 0.84 V, which is among the highest one in the reported copolymers based on BDT and TT units, leading to an enhanced PCE of 8.42%. The results indicate that molecular modification by introducing alkylthio side chain will be a promising strategy to broaden the absorption, down-shift the HOMO energy level and increase the hole mobility of the low band gap 2D-conjugated polymers for further enhancing the photovoltaic performance of PSCs. PBDTT-O-TT-C and PBDTT-S-TT-C were developed to further study the conclusion. We found that OSC device based on PBDTT-S-TT-C with alkylthio side chain also demonstrated a high Voc of 0.89 V, with a PCE of 6.85% when processed with 3% DIO additive

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Chen, Jie. "Spectroscopic Ellipsometry Studies of II-VI Semiconductor Materials and Solar Cells." University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1286813480.

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42

Yu, Fei. "Graphene-enhanced Polymer Bulk-heterojunction Solar Cells." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439310775.

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43

Kang, Moon Hee. "Development of high-efficiency silicon solar cells and modeling the impact of system parameters on levelized cost of electricity." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47647.

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The objective of this thesis is to develop low-cost high-efficiency crystalline silicon solar cells which are at the right intersection of cost and performance to make photovoltaics (PV) affordable. The goal was addressed by improving the optical and electrical performance of silicon solar cells through process optimization, device modeling, clever cell design, fundamental understanding, and minimization of loss mechanisms. To define the right intersection of cost and performance, analytical models to assess the premium or value associated with efficiency, temperature coefficient, balance of system cost, and solar insolation were developed and detailed cost analysis was performed to quantify the impact of key system and financial parameters in the levelized cost of electricity from PV.

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44

Ho, Po Yu. "New molecular materials for organic and dye-sensitized solar cells and photocatalytic hydrogen generation." HKBU Institutional Repository, 2016. https://repository.hkbu.edu.hk/etd_oa/280.

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Emerging solar energy technology, including photovoltaics, solar fuels generation and solar thermal systems, is considered as one of the most potential renewable energy resources because of the tremendous and free radiant energy supply by our sun. Unlike burning of fossil fuels, carbon dioxide emission-free energy conversion process is definitely another key feature and attracting scientists to explore these research areas. Besides, this implies a giant business market to compete with traditional fossil fuel companies. Nevertheless, it is too early to realize commercial application since the technologies are in the early development stage and there is still much room to explore and improve. Simply speaking, energy conversion efficiency, robustness, environmental impacts and cost are the major factors the community should deeply concentrate on at this moment. This provides many research opportunities on the creation of novel molecular functional materials and investigates the relationship between the molecular design and functional properties, and they obviously take up significant roles in the technology evolution. The basic concepts and conspectuses regarding organic photovoltaics and light-driven hydrogen generation are collected in Chapter 1. In Chapter 2, a series of new thiophene-based small molecules is presented and the discussion is focused on its application in the bulk-heterojunction organic solar cells. Importantly, the structure-property relationship is elucidated by varying the terminal electron withdrawing group and elongating the central electron donating unit. The highest power conversion efficiency (η) of 2.6% is attained by the device with compound M3 as the active material with traditional device configuration (without any annealing process and additives addition) under AM 1.5G irradiation. In Chapter 3, a series of DπA organic dyes is introduced and the discussion concentrates on its application in the dye-sensitized solar cells. Briefly, a case study on alkyl chain effects is investigated while a new starburst triarylamine donor and uncommon selenophene-containing π-linker are studied separately. The highest power conversion efficiency (η) of 6.7% is achieved by D11 under AM 1.5G irradiation with a high open-circuit voltage of 0.825 V. In Chapter 4, three new platinum(II) diimine complexes are synthesized and they are utilized as photosensitizers with platinized titanium dioxide as catalyst site in the context of light-driven hydrogen generation. Comparison between platinum(II) diimine dithiolate complex and platinum(II) diimine bis(acetylide) complex is accomplished, and the importance of photosensitization using an organic chromophore with a desirable energy transfer consideration is accounted. Finally, Chapter 5 puts forward the concluding remarks and possible future works while Chapter 6 includes all the experimental details of the studied compounds presented in Chapter 24.

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45

Sheng, Xing Ph D. Massachusetts Institute of Technology. "Thin-film silicon solar cells : photonic design, process and fundamentals." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/105936.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2012.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 153-159).
The photovoltaic technology has been attracting widespread attention because of its effective energy harvest by directly converting solar energy into electricity. Thin-film silicon solar cells are believed to be a promising candidate for further scaled-up production and cost reduction while maintaining the advantages of bulk silicon. The efficiency of thin-film Si solar cells critically depends on optical absorption in the silicon layer since silicon has low absorption coefficient in the red and near-infrared (IR) wavelength ranges due to its indirect bandgap nature. This thesis aims at understanding, designing, and fabricating novel photonic structures for efficiency enhancement in thin-film Si solar cells. We have explored a previously reported a photonic crystal (PC) based structure to improve light absorption in thin-film Si solar cells. The PC structure combines a dielectric grating layer and a distributed Bragg reflector (DBR) for effcient light scattering and reflection, increasing light path length in the thin-film cell. We have understood the operation principles for this design by using photonic band theories and electromagnetic wave simulations. we discover that this DBR with gratings exhibit unusual light trapping in a way different from metal reflectors and photonic crystals. The light trapping effects for the DBR with and without reflector are numerically investigated. The self-assembled anodic aluminum oxide (AAO) technique is introduced to non- lithographically fabricate the grating structure. We adjust the AAO structural parameters by using different anodization voltages, times and electrolytes. Two-step anodization is employed to obtain nearly hexagonal AAO pattern. The interpore periods of the fabricated AAO are calculated by fast Fourier transform (FFT) analysis. We have also demonstrated the fabrication of ordered patterns made of other materials like amorphous Si (a-Si) and silver by using the AAO membrane as a deposition mask. Numerical simulations predict that the fabricated AAO pattern exhibits light trapping performance comparable to the perfectly periodic grating layer. We have implemented the light trapping concepts combining the self-assembled AAO layer and the DBR in the backside of crystalline Si wafers. Photoconductivity measurements suggest that the light absorption is improved in the near-IR spectral range near the band edge of Si. Furthermore, different types of thin-film Si solar cells, including a-Si, mi- crocrystalline Si ([mu]-Si) and micromorph Si solar cells, are investigated. For demonstration, the designed structure is integrated into a 1:5 [mu]m thick [mu]c-Si solar cell. We use numerical simulations to obtain the optimal structure parameters for the grating and the DBR, and then we fabricate the optimized structures using the AAO membrane as a template. The prototype devices integrating our proposed backside structure yield a 21% improvement in efficiency. This is further verified by quantum efficiency measurements, which clearly indicate stronger light absorption in the red and near-IR spectral ranges. Lastly, we have explored the fundamental light trapping limits for thin-film Si solar cells in the wave optics regime. We develop a deterministic method to optimize periodic textures for light trapping. Deep and high-index-contrast textures exhibit strong anisotropic scattering that is outside the regime of validity of the Lambertian models commonly used to describe texture-induced absorption enhancement for normal incidence. In the weak ab- sorption regime, our optimized surface texture in two dimensions (2D) enhances absorption by a factor of 2.7[pi]n, considerably larger than the classical [pi]n Lambertian result and exceeding by almost 50% a recent generalization of Lambertian model for periodic structures in finite spectral range. Since the [pi]n Lambertian limit still applies for isotropic incident light, our optimization methodology can be thought of optimizing the angle/enhancement tradeoff for periodic textures. Based on a modified Shockley-Queisser theory, we conclude that it is possible to achieve more than 20% efficiency in a 1:5 [mu]m thick crystalline Si cell if advanced light trapping schemes can be realized.
by Xing Sheng.
Ph. D.

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46

Hansson, Rickard. "Materials and Device Engineering for Efficient and Stable Polymer Solar Cells." Doctoral thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-47257.

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Polymer solar cells form a promising technology for converting sunlight into electricity, and have reached record efficiencies over 10% and lifetimes of several years. The performance of polymer solar cells depends strongly on the distribution of electron donor and acceptor materials in the active layer. To achieve longer lifetimes, degradation processes in the materials have to be understood. In this thesis, a set of complementary spectroscopy and microscopy techniques, among which soft X-ray techniques have been used to determine the morphology of polymer:fullerene based active layers. We have found that the morphology of TQ1:PC70BM films is strongly influenced by the processing solvent and the use of solvent additives. We have also found, by using soft X-ray techniques, that not only the light-absorbing polymer TQ1, but also the fullerene is susceptible to photo-degradation in air. Moreover, the fullerene degradation is accelerated in the presence of the polymer. Additionally, this thesis addresses the role of the interfacial layers for device performance and stability. The commonly used hole transport material PEDOT:PSS has the advantage of being solution processable at room temperature, but this layer is also known to contribute to the device degradation. We have found that low-temperature processed NiOx is a promising alternative to PEDOT:PSS, leading to improved device performance. Even for encapsulated polymer solar cells, some photo-induced degradation of the electrical performance is observed and is found to depend on the nature of the hole transport material. We found a better initial stability for solar cells with MoO3 hole transport layers than with PEDOT:PSS. In the pursuit of understanding the initial decrease in electrical performance of PEDOT:PSS-based devices, simulations were performed, from which a number of degradation sources could be excluded.
With the increasing global demand for energy, solar cells provide a clean method for converting the abundant sunlight to electricity. Polymer solar cells can be made from a large variety of light-harvesting and electrically conducting molecules and are inexpensive to produce. They have additional advantages, like their mechanical flexibility and low weight, which opens opportunities for novel applications. In order for polymer solar cells to be more competitive, however, both the power conversion efficiencies and lifetimes need to further improve. One way to achieve this is to optimize the morphology of the active layer. The active layer of a polymer solar cell consists of electron donating and electron accepting molecules whose distribution in the bulk of the film is a major factor that determines the solar cell performance. This thesis presents the use of complementary spectroscopy and microscopy methods to probe the local composition in the active layer of polymer solar cells. The stability of the active layer is studied and the interplay between the photo-degradation of the donor and acceptor molecules is investigated. Additionally, this thesis addresses how the interfacial layers between the active layer and the electrodes can influence device performance and stability.

I publikationen felaktigt ISBN 978-91-7063-739-1

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47

Prönneke, Liv [Verfasser], and Jürgen [Akademischer Betreuer] Werner. "Fluorescent materials for silicon solar cells / Liv Prönneke. Betreuer: Jürgen Werner." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2012. http://d-nb.info/102604359X/34.

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48

Castellanos, Rodriguez Sergio. "Electrical impact assessment of dislocations in silicon materials for solar cells." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101529.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 117-133).
Cast multicrystalline silicon (mc-Si) makes up about 60% of the global photovoltaics market production, and is favored due to its lower areal and capex costs relative to monocrystalline silicon. This method, however, produces material with a higher density of defects (e.g., dislocations, grain boundaries, metal impurities) than more expensive single-crystalline growth methods. A higher density of defects, particularly dislocations, results in a greater density of charge-carrier recombination centers, which reduce a solar cell's efficiency. Interestingly, the recombination activity of individual dislocations and dislocation clusters can vary by orders of magnitude, even within the same device and a separation of only by millimeters of distance. In this thesis, I combine a surface-analysis approach with bulk characterization techniques to explore the underlying root cause of variations in recombination activity between different dislocation clusters. I propose and validate an optical inspection routine based on dislocations' surface characteristics to predict their recombination activity, and extend this methodology to novel growth processes. Lastly, I explore a spatial dispersion metric to assess its potential as a descriptor for the electrical recombination activity of clusters in silicon. This work provides tools to crystal growers and solar cell manufacturers that facilitate the evaluation of electrical performance at early stages of the cell processing, enabling them to reduce the time required for cycles of learning to improve crystal growth processes.
by Sergio Castellanos-Rodríguez.
Ph. D.

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49

Tessarolo, Marta <1985&gt. "Organic Bulk Heterojunction Solar Cells: Materials Properties Device Stability And Performance." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7266/.

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In the field of Photovoltaic technologies the organic solar cells are particularly attractive because of their ease of processing, mechanical flexibility and potential low cost production techniques. So far, the reported efficiencies are not high enough to allow to be competitive in the market, however with the introduction of new photoactive materials, device architectures and light management structures, the power conversion efficiencies, at laboratory scale, has rapidly reached the 12%, showing a great potential and a bright future for organic solar cells. Nevertheless, in view of commercial products, two main problems are still unresolved: the relatively low performance of the modules and their lifetime. In sight of this, the present Ph.D thesis has a double goal: 1) a better understanding of the relationship between devices performance and photoactive materials structures 2) a deep investigation on device degradation processes, with particular attention on the effects induced by temperature and incident light. As a result, promising approaches to further optimize the polymer’s optoelectrial properties, and thus the corresponding device performance, are proposed. About the lifetime, first the thermal degradation mechanisms involved on the active layer was investigated and it has been demonstrated the role of the other layers and interfaces in the solar cell thermal stability. In this contest an innovative fast capacitance based thermal test has been developed in order to obtain information regarding the limit operating temperature above which the device becomes thermally unstable. In the end, a preliminary study on the photostability issue was carried out demostrating that the photodegradation of organic solar cells not depends just on the photostability of the donor polymer, but is connected also with the composition of the active layer solution and on the interaction with the adjacent layers. Solutions to limit or prevent the devices degradation processes are proposed.

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Xiong, Wanshu. "Novel optically tunable materials for photonic applications : lasers and solar cells." Thesis, University of Bristol, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761237.

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Dissertations / Theses on the topic 'Solar cells – Materials'

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