Dissertations / Theses on the topic 'Inorganic Hybrid Heterostructure Solar Cells'

The purpose of this work is to develop organic/inorganic hybrid solar cells based on electroplated CdTe. The materials used in this research are CdS, CdTe and PAni. These materials have been characterised by XRD, Raman spectroscopy, EDX, SEM, AFM, UV-Vis spectroscopy, PEC, C-V and DC measurements, UPS and PL for their structural, compositional, morphological, optical, electrical and defect properties. CdS has electrodeposited from the electrolyte using (NH[4])[2]S[2]O[3] as the sulphur source. The optimum growth voltage (V[g]) and temperature (T[g]) are obtained at 1455 mV and 85°C, respectively. The best annealing condition is found to be at 400°C for 20 minutes in the presence of CdCl[2]+CdF[2]. CdTe thin films were electrodeposited from CdCl[2] precursor and a comprehensive study was carried out for the first time. The work has demonstrated a better understanding of material issues and some clues on the effect of CdCl[2] treatment. The optimum V[g] and annealing condition were obtained at 698 mV with respect to the calomel electrode and 420°C for 20 minutes in the presence of CdCl[2]+CdF[2] or CdCl[2]+CdF[2]+GaCl[3]. The development of PAni thin films has been established using anodic and cathodic deposition. The pernigraniline salt PAni grown from anodic has an amorphous structure, large bandgap and cementing growth effect while leucoemeraldine salt PAni grown from cathodic deposition shows the best crystallinity at V[g]=1654 mV with respect to carbon anode, smaller grain size, higher resistivity and lower bandgap. The CdS, CdTe and PAni thin films have been studied in device structures, assessing their solar cell device performance. The best of CdS/CdTe solar cell was observed with efficiency of 5.8% when using CdS thin film treated with CdCl[2]+CdF[2] at 400°C. The best solar cell from CdTe study shows the efficiency of 6.8% when using CdTe thin films treated with CdCl[2]+CdF[2] at 420°C. Further study demonstrates that a device with g/FTO/n-CdS(~200 nm)/n-CdTe(~1200 nm)/p-CdTe(~300 nm)/Au shows high J[sc] and highest efficiency (7.7%) due to the formation of n-n heterojunction, p-n homojuction and ohmic contact within the structure. The efficiency of the solar cell increased from -2.4% to -4.2% when incorporating -81 nm thick PAni layer grown from anodic deposition. The devices incorporating ZnS, ZnTe and CdSe layers show the prospect of graded bandgap solar cell, but proper optimisation on each material should be carried out before using in multi-layer device structures. The study on the lifetime of solar cells show slow degradation and it maintained more than 83% of its initial efficiency after 9,000 hours.

Solar energy as the most abundant source of energy is clean, non-pollutant, and completely renewable, which provides energy security, independence, and reliability. Organic-inorganic hybrid perovskite solar cells (PSCs) revolutionized the photovoltaics field not only by showing high efficiency of above 22% in just a few years but also by providing cheap and facile fabrication methods. In this dissertation, fabrication of PSCs in both ambient air conditions and environmentally controlled N2-filled glove-box are studied. Several characterization methods such as SEM, XRD, EDS, Profilometry, four-point probe measurement, EQE, and current-voltage measurements were employed to examine the quality of thin films and the performance of the PSCs. A few issues with the use of equipment for the fabrication of thin films are addressed, and the solutions are provided. It is suggested to fabricate PSCs in ambient air conditions entirely, to reduce the production cost. So, in this part, the preparation of the solutions, the fabrication of thin films, and the storage of materials were performed in ambient air conditions regardless of their humidity sensitivity. Thus, for the first part, the fabrication of PSCs in ambient air conditions with relative humidity above ~36% with and without moisture sensitive material, i.e., Li-TFSI are provided. Perovskite materials including MAPbI3 and mixed cation MAyFA(1-y)PbIxBr(1-x) compositions are investigated. Many solution-process parameters such as the spin-coating speed for deposition of the hole transporting layer (HTL), preparation of the HTL solution, impact of air and light on the HTL conductivity, and the effect of repetitive measurement of PSCs are investigated. The results show that the higher spin speed of PbI2 is critical for high-quality PbI2 film formation. The author also found that exposure of samples to air and light are both crucial for fabrication of solar cells with larger current density and better fill factor. The aging characteristics of the PSCs in air and vacuum environments are also investigated. Each performance parameter of air-stored samples shows a drastic change compared with that of the vacuum-stored samples, and both moisture and oxygen in air are found to influence the PSCs performances. These results are essential towards the fabrication of low-cost, high-efficiency PSCs in ambient air conditions. In the second part, the research is focused on the fabrication of high-efficiency PSCs using the glove-box. Both single-step and two-step spin-coating methods with perovskite precursors such as MAyFA(1-y)PbIxBr(1-x) and Cesium-doped mixed cation perovskite with a final formula of Cs0.07MA0.1581FA0.7719Pb1I2.49Br0.51 were considered. The effect of several materials and process parameters on the performance of PSCs are investigated. A new solution which consists of titanium dioxide (TiO2), hydrochloric acid (HCl), and anhydrous ethanol is introduced and optimized for fabrication of quick, pinhole-free, and efficient hole-blocking layer using the spin-coating method. Highly reproducible PSCs with an average power conversion efficiency (PCE) of 15.4% are fabricated using this solution by spin-coating method compared to the conventional solution utilizing both spin-coating with an average PCE of 10.6% and spray pyrolysis with an average PCE of 13.78%. Moreover, a thin layer of silver is introduced as an interlayer between the HTL and the back contact. Interestingly, it improved the current density and, finally the PCEs of devices by improving the adhesion of the back electrode onto the organic HTL and increasing the light reflection in the PSC. Finally, a highly reproducible fabrication procedure for cesium-doped PSCs using the anti-solvent method with an average PCE of 16.5%, and a maximum PCE of ~17.5% is provided.

Au catalyst ZnO nanostructures have been grown on the a- and c-plane sapphire substrate by PLD. Influence of substrate lattice orientation, substrate surface and different substrate annealing temperature have been characterized by AFM, SEM and XRD. This report shows that a-plane sapphire substrate annealed at 1000 degree C and 1200 degree C improves the growth condition of Au catalyst ZnO nanostructures. For c-plane sapphire; annealing at 1200 degree C and 1400 degree C enhances the nanostructure growth. The better growth condition is a result of the terrace-and-step morphology seen on the substrate surface prior to growth. This report also indicates a correlation between the azimuthal in-plane alignment of the grown nanostructures and the sapphire substrate lattice orientation.

[ES] Las perovskitas orgánicas-inorgánicas de haluros de metilamonio y plomo y sus mezclas han mostrado propiedades optoelectrónicas óptimas como absorbente ideal para aplicaciones fotovoltaicas. Los dispositivos solares basados en perovskita han evolucionado rápidamente, desde una eficiencia del 3.9% en 2009, al 22.7% en 2017 y con un coste de fabricación más bajo que las células solares de silicio. Una desventaja del uso de absorbentes de perovskita en dispositivos fotovoltaicos es su baja estabilidad. Las células con un alto rendimiento, pierden su eficiencia y se degradan rápidamente. Para poder producir estos materiales industrialmente es necesario realizar estudios en profundidad que mejoren la eficiencia y estabilidad. Una vía de mejora es la ingeniería composicional, estrategia que hemos empleado en la elaboración de esta tesis y que consiste en la investigación y mejora de las propiedades optoelectrónicas y morfológicas, derivadas de la sustitución y/o combinación de cationes y aniones, que constituyen el material de perovskita. Se sintetizaron polvos puros de perovskita de I, Br, Cl, a partir de los cuales se prepararon capas puras y mixtas MAPbX3-xYx, con el objetivo de mejorar sus propiedades optoelectrónicas y estructurales. Los análisis de difracción de rayos X mostraron las propiedades estructurales de los polvos cristalinos y capas puras y mixtas. Los análisis de UV-vis y fotoluminiscencia mostraron que el rango de absorción varía a lo largo del espectro visible en función del contenido del haluro en las capas. Los análisis de fotoluminiscencia y calorimetría diferencial de barrido muestran los cambios de fase de las perovskitas puras a distintas temperaturas, coincidiendo dichos cambios en ambos análisis. El análisis FESEM de las perovskitas puras mostró las diferencias morfológicas entre los polvos y capas. Siguiendo esta línea de investigación, se estudiaron con más detalle las perovskitas mixtas de yodo-bromo, con un contenido de bromo de hasta el 33%, consiguiendo ajustar el bandgap para evitar pérdidas en la absorción y mejorar las propiedades optoelectrónicas, estructurales y morfológicas. A pesar de las buenas propiedades optoelectrónicas de las perovskitas de metilamonio, el catión orgánico disminuye su estabilidad, lo que llevó a investigar otros cationes inorgánicos. Las perovskitas de cesio son una alternativa prometedora, y por esta razón hemos sintetizado capas finas de perovskitas de cesio mixtas, CsPbBr3-xIx, para determinar los efectos que produce la sustitución parcial del yodo en las propiedades físicas y la estabilidad. Se obtuvieron capas con una buena resistencia a la humedad y temperatura, favoreciendo su aplicación en el campo fotovoltaico. Se ha estudiado la sustitución parcial del catión de metilamonio con otros cationes orgánicos, como el guanidinio e imidiazolio. Se demostró que pequeñas cantidades de guanidinio mejoran la estabilidad de las capas y su morfología. Se estableció el límite de solubilidad del guanidinio en el 20%, aproximadamente, y se determinó la estructura cristalina de las mezclas. La intensidad del pico de fotoluminiscencia aumentó para mezclas por debajo del límite de solubilidad. Se obtuvieron resultados similares para la sustitución del metilamonio con pequeñas cantidades de imidazolio. Los análisis de rayos X establecieron el límite de solubilidad en aproximadamente el 10% y una mejora en la cristalinidad. Los resultados de fotoluminiscencia sugieren que pequeñas cantidades de imidazolio reducen significativamente las recombinaciones no radiativas, actuando como un pasivador efectivo. Finalmente, se muestra el proceso de fabricación de dispositivos basados en MAPbI3 y sintetizados en función de las condiciones ambientales y empleando el dietil éter como anti-solvente. Los dispositivos mostraron una eficiencia máxima del 14.73%. Se ha probado que la oxidación del spiro-OMeTAD, bajo condiciones cont
[FR] Les perovskites orgàniques-inorgàniques de halurs de metilamoni i plom i les seues mescles han mostrat propietats optoelectròniques òptimes com a absorbent ideal per a aplicacions fotovoltaiques. Els dispositius solars basats en perovskita han evolucionat ràpidament, passant d'una eficiència del 3.9% en 2009, fins al 22.7% en 2017, i amb un cost de fabricació més baix que les cèl·lules solars de silici. No obstant això, un dels desavantatges de l'ús de absorbents de perovskita és la baixa estabilitat. En general, les cèl·lules que mostren un alt rendiment, perden la seua eficiència i es degraden ràpidament. Per a que aquestos materials puguen ser produits industrialment a gran escala és necessari estudiar-los en profunditat per millorar la eficiència i estabilitat. Una de les vies de millora és l'enginyeria composicional, estratègia que hem emprat en l'elaboració d'aquesta tesi i que consisteix en la investigació i la millora de les propietats optoelectròniques i morfològiques, derivades de la substitució i/o combinació de cations i anions, que constitueixen el material de perovskita. S'han sintetitzat pols purs de perovskita per a I, Br, Cl, a partir d'els quals es van preparar capes pures i mixtes MAPbX3-xYx per a millorar les propietats optoelectròniques i estructurals. Mitjançant anàlisi de difracció de raigs X, s'estudiaren les propietats estructurals del pols cristalins i capes pures i mixtes. Els anàlisis d'UV-vis i fotoluminiscència, mostren que el rang d'absorció varia al llarg de l'espectre visible en funció del contingut de l'halur. Les anàlisis de fotoluminiscència i calorimetria diferencial mostren els canvis de fase de les perovskites pures a diferents temperatures, coincidint aquestos canvis en totes dues anàlisis. L'anàlisi FESEM de les perovskites pures, mostra les diferències morfològiques entre els pols i capes. Seguint aquesta línia d'investigació, s'estudiaren les perovskites mixtes de iode-brom, amb un contingut de brom de fins el 33%, ajustant el bandgap per a evitar pèrdues en l'absorció i millorar les propietats optoelectròniques, estructurals i morfològiques. Malgrat les bones propietats optoelectròniques de les perovskites de metilamoni, el catió orgànic disminueix la estabilitat, la qual cosa ha portat a investigar l'ús d'altres cations inorgànics. Les perovskites de cesi són una alternativa prometedora, i per aquesta raó hem sintetitzat capes fines de perovskites de cesi mixtes, CsPbBr3-xIx, per tal de determinar els efectes de la substitució parcial del iode en les propietats físiques i l'estabilitat. Es van obtenir capes amb una bona resistència a la humitat i a la temperatura, afavorint la seua aplicació en el camp fotovoltaic. S'ha estudiat també la substitució parcial del catió de metilamoni amb altres cations orgànics, com el guanidini i imidiazoli. S'ha demostrat que petites quantitats de guanidini milloren l'estabilitat i la morfologia de les capes. S'ha establert que el límit de solubilitat del guanidini es del 20%, aproximadament, i s'ha determinat l'estructura cristal·lina de les mescles. S'ha observat un augment en la intensitat del pic de fotoluminiscència per a mescles per sota del límit de solubilitat. Es van obtenir resultats similars per a la substitució del metilamoni amb petites quantitats de imidazoli. Les anàlisis de difracció de raigs X van establir el límit de solubilitat en aproximadament el 10% i una millora en la cristalinitat. Els resultats de fotoluminiscència suggereixen que petites quantitats de imidazoli redueixen les recombinacions no radiatives, actuant com un pasivador efectiu. Finalment, es mostra el procés de fabricació de dispositius basats en MAPbI3 i sintetitzats en funció de les condicions ambientals, especialment la humitat relativa i utilitzant el dietil èter com anti-solvent. Els dispositius van mostrar una eficiència màx
[EN] Organic-inorganic methylammonium lead halides perovskites and their mixtures have shown optimal optoelectronic properties as an ideal absorber for photovoltaic applications. In the last decade, solar devices based on perovskite have evolved rapidly, going from an initial efficiency of only 3.9% in 2009, to an efficiency of 22.7% in 2017 and being, at the same time, more cost-effective than silicon solar cells. However, one of the main disadvantages when using perovskite absorbents in photovoltaic devices is their low stability. In general, cells that show high performance lose their efficiency and degrade rapidly. For these materials to be scalable it is necessary to carry out in-depth studies aiming at improved efficiency and stability. One of the main sources to improve stability and efficiency is compositional engineering, a strategy employed in the elaboration of this thesis, consisting of the investigation and improvement of the optoelectronic and morphological properties, derived from the substitution and / or combination of cations and anions, which constitute the perovskite material. Pure powders of perovskite were synthesized, for I, Br, Cl, from which pure and mixed MAPbX3-xYx films were prepared in order to improve their optoelectronic and structural properties. By means of X-ray diffraction analysis, the structural properties of crystalline powders and pure and mixed films were studied. Employing UV-vis and photoluminescence analysis, it was observed that the absorption range varied along the visible spectrum as a function of the halide content in the thin films. Both, photoluminescence and differential scanning calorimetry analysis showed the changes of phase of the pure perovskites at different temperatures. FESEM characterization of the pure perovskites showed the morphological differences between the powders and the films. Following this line of research, mixed perovskites of iodine-bromine with a bromine content of up to 33% were studied in more detail. The bandgap was tuned to avoid significant losses in absorption and improve the optoelectronic, structural and morphological properties. Despite the excellent optoelectronic properties of the methylammonium perovskite, the presence of the organic cation decreases its stability, which prompted research into the use of other inorganic cations. Cesium perovskites, are a very promising alternative, and for this reason we synthesized thin films of mixed cesium perovskites, CsPbBr3-xIx, to determine the effects of the partial substitution of iodine on physical properties and stability. Films with a very good resistance to moisture and temperature were obtained, which will favor the application of this type of perovskites in the photovoltaic field. The partial replacement of the methylammonium cation with other organic cations, such as guanidinium and imidiazolium, was also studied, showing that small amounts of guanidinium significantly improve the stability of the films and their morphology. It was established that the solubility limit of guanidinium is approximately 20%, and the crystalline structure of the mixtures was determined. An increase in the intensity of the photoluminescence peak for mixtures below the solubility limit was observed. Similar results were obtained for the substitution of methylammonium with small amounts of imidazolium. X-ray diffraction analyzes established the solubility limit at approximately 10% and an improvement in crystallinity. Photoluminescence results suggest that small amounts of imidazolium significantly reduce nonradiative recombinations, acting as an effective passivator. Finally, the manufacturing process of devices based on MAPbI3 and synthesized according to environmental conditions, especially relative humidity and using diethyl ether as anti-solvent is shown. The devices presented a maximum efficiency of 14.73%, proving that the oxidation of spiro-OMeTAD, under controlled humidity conditions, can improve efficiency.
Vega Fleitas, E. (2018). Study and Characterization of Hybrid Organic-Inorganic Perovskites for Solar Cells Applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/113402
TESIS

Solar cells involving two different perovskites were manufactured and analyzed. The perovskites were (CH3NH3)PbI3 and (CH3NH3)SnI3. Both perovskites have a shared methyl ammonium group (MA) and are used as both light absorbing material and hole conducting material (HTM) in this project. The preparation procedures for the complete device were according to previous attempts to make stable organic-inorganic hybrid perovskites and involved different layers and procedures. Both perovskites were manufactured by mixing methyl ammonium iodide with either lead iodide or tin iodide in different concentrations. This was then deposited on a 600nm thick mesoporous TiO2 layer. Deposition of the hole-transporting material (HTM) was done by spin-coating 2,2´,7,7´-tetrakis-(N,N-dip-methoxyphenylamine) 9,9´-spirobifluorene, also called spiro-OMeTAD. Lastly thermal evaporation was used to deposit a silver electrode. Different measurements were done on the light absorbing materials. The lead perovskite solar cell device was subjected to illumination with Air Mass 1.5 sunlight (100mW/cm2) which produced an open circuit voltage Voc of 0.645 V, a short circuit photocurrent Jsc of about 7 mA/cm2, and a fill factor FF of 0.445. This resulted in a power conversion efficiency (PCE) of about 2% and an incident photon to current efficiency (IPCE) of up to 60%. The tin perovskite has not been used in solar cells before and the initial results presented here shows low performance using the same device construction as for the lead perovskite. However, the incident photon to electron conversion affirms that there is a current in the visible region, and IPCE of 12.5 % was observed at 375nm. UV-visible NIR measurement was used to analyze the light absorption of the perovskite structures and a broader light absorption was observed for the lead perovskite compared to the tin perovskite. X-ray diffraction (XRD) analyzing was done on both perovskite materials using different concentrations and both with and without nanoporous TiO2 film. Both perovskites demonstrate very similar peaks with some exceptions. Photo-induced absorption (PIA) measurement was used for the purpose of showing the magnitude of charge separation or hole transfer in the light absorbing material, both when using the perovskites as a light absorber and a hole conductor. This is measured by analyzing the hole injection from the excited light absorber into the HTM. Hole transfer was observed for the lead perovskite (when used as light absorber) and tin perovskite (when used as hole conductor).

Hybrid organic-inorganic solar photovoltaic (PV) cells capable of directly converting sunlight to electricity have attracted much attention in recent years. Despite evident technological advancements in the PV industry, the widespread commercialisation of solar cells is still being mired by their low conversion efficiencies and high cost per Watt. Perovskites are an emerging class of semiconductors providing a low-cost alternative to silicon-based photovoltaic cells, which currently dominate the market. This thesis develops a series of studies on “all-solid state perovskite solar cells” fabricated via vapour deposition which is an industrially-accessible technique, to achieve planar heterojunction architectures and efficient PV devices. Chapter 2 presents a general outlook on the operating principles of solar cells, delving deeper into the specific operational mechanism of perovskite solar cells. It also explores the usual methods employed in the fabrication of perovskite thin films. Chapter 3 describes the experimental procedures followed during the fabrication of the individual components constituting the device from the synthesis of the precursors to the construction of the functioning perovskite PV devices. Chapter 4 demonstrates pioneering work involving the dual-source vapour deposition (DSVD) of planar heterojunction perovskite solar cells which generated remarkable power conversion efficiency values surpassing 15%. These significant results pave the way for the mass-production of perovskite PVs. To further expand the range of feasible vapour deposition techniques, a two-layer sequential vapour deposition (SVD) technique is explored in Chapter 5. This chapter focusses on identifying the factors affecting the fundamental properties of the vapour-deposited films. Findings provide an improved understanding of the effects of precursor compositions and annealing conditions on the films. Chapter 5 concludes with a comparison between SVD and DSVD fabricated films, highlighting the benefits of each vapour deposition technique. Furthermore, hysteretic effects are analysed in Chapter 6 for the perovskite PV devices fabricated based on different structural configurations. An interesting discovery involving the temporary functioning of compact layer-free perovskite PV devices suggests the presence of a built-in-field responsible for the hysteresis of the cells. The observations made in this chapter yield a new understanding of the functionality of individual cell layers. Combining the advantages of the optimum vapour deposition technique established in Chapter 4 and Chapter 5, with the enhanced understanding of perovskite PV cell operational mechanism acquired from Chapter 6, an ongoing study on an “all-perovskite” tandem solar cell is introduced in Chapter 7. This demonstration of the “all-perovskite” tandem devices confirms the versatility of perovskites for a broader range of PV applications.

Organic and hybrid organic-inorganic photovoltaic (PV) devices have the potential to provide low-cost, large scale renewable energy. Despite the tremendous progress that has been made in this field, device efficiencies remain low. This low efficiency can be partly attributed to the low open-circuit voltages (Voc) generated by organic and hybrid organic-inorganic PV devices. The Voc is critically determined by the energy-level alignment at the interface between the materials forming the device. In this thesis we use first-principles methods to explore the energy-level alignment at the interfaces between the conjugated polymer poly(3-hexylthiophene) (P3HT) and three electron acceptors, zinc oxide (ZnO), gallium arsenide (GaAs) and graphene. We find that Voc reported in the literature for ZnO/P3HT devices is significantly lower than the theoretical maximum and that the interfacial electrostatic dipole plays an important role in the physics underlying the charge transfer at the heterojunction. We note significant charge transfer from the polymer to the semiconductor at GaAs/P3HT interfaces, and use this result to help interpret experimental data. Our findings support the conclusion that charge transferred from P3HT to GaAs nanowires can passivate the surface defect states of the latter and, as a result, account for the observed decrease in photoluminescence lifetimes. Finally, we explore the energy-level alignment at the graphene/P3HT interface and find that Voc reported for experimental devices is in line with the theoretical maximum. The effect of functionalised graphene is also examined, leading to the suggestion that functionalisation might have important consequences for device optimisation.

This thesis consists of three main studies: magnetic field effects in thermally activated delayed fluorescent (TADF) organic light emitting diodes (OLEDs), magnetic field effects in bipolar and unipolar polythiophene (P3HT) devices and a study of hybrid organic/inorganic perovskite devices. Spin-dependent transport and recombination processes of spin-pair species have been detected by magnetic field effect (MFE) technique in carbon-based semi- conductor devices. Magneto-electroluminescence (MEL) and magneto-conductivity have been measured as a function of the applied magnetic field, B, in light emitting diodes. TADF materials have been used instead of simple fluorescent materials in OLEDs. We have observed very large magnetic response with TADF materials. The second study is magnetic field effects of regio-regular P3HT based OLED devices. P3HT is a well known semiconducting polymer, and its electrical properties such as magneto-conductance can be affected by an applied magnetic field. P3HT was chosen because it exhibits a sign change in magnetoresistance (MR) as the bias is increased. Unipolar and bipolar devices have been fabricated with different electrode materials to understand which model can be best to explain organic magnetoresistance effect, possibly depending on the operating regime of the device. Transport and luminescence spectroscopies were studied to isolate the different mechanisms and identify their fingerprints. The third study is on hybrid organic-inorganic perovskite devices. With the potential of achieving very high efficiencies and the very low production costs, perovskite solar cells have become commercially attractive. Scanning electron microscopy (SEM) images and absorption spectrum of the films were compared in single-step solution, two-step solution and solution-assisted vapor deposition techniques. Grain size, morphology and thickness parameters of perovskite films were studied within these techniques. Perovskite solar cells were fabricated and their efficiencies were measured.

New thin-film solar cell materials and a greater understanding of their properties are needed to meet the urgent demand for sustainable, lower-cost and scalable photovoltaics. Computational techniques have been used to investigate Cu2ZnSnS4, CuSbS2 and CuBiS2 , which are potential absorber layer materials in thin-film photovoltaics. Their low cost, low toxicity and their constituent’s relative abundance make them suitable replacements for current thin-film absorbers, which are CdTe or Cu(In, Ga)(S, Se)2 based systems. Firstly, we have used hybrid Density Functional Theory (DFT) calculations to study CuSbS2 and CuBiS2. We calculate band gaps of 1.69 eV and 1.55 eV respectively, placing CuBiS2 within the optimal range for a viable absorber material. The density of states for both these materials indicate that formation of electron hole charge carriers will occur in the Cu d10 band. Consequently, photoexcitation leads to the oxidation of Cu(I). Secondly, we have derived interatomic potentials which describe the complex structure of Cu2ZnSnS4 accurately. We find that the Cu/Zn antisite defect represents the lowest energy form of intrinsic defect disorder. For these antisite defects, we find a preference for small neutral defect clusters, which suggests a degree of self-passivation exists. Investigations of Cu-ion transport find VCu migration is possible via a vacancy hopping mechanism. There are pathways which can be connected to give 3D long-range diffusion. Investigations of the Cu/Zn site disorder in Cu2ZnSnS4 find that configurations which are kesterite-like will dominate synthetic samples. However, perfectly ordered kesterite will not be formed due to entropic effects. The simulations indicate the stannite and stannite-like polymorphs are less favourable, and can only account for ≈2.5% of a sample. Investigations of the surfaces of Cu2ZnSnS4, suggest that the vast majority of the low index surfaces are dipolar and that only the (1 1 2), (0 1 0) and (1 0 1) surfaces have low surface energies.

Perovskite-solceller är en framväxande och lovande tunnfilmsteknik, som uppnådde hög effektivitet på en ofantlig kort tid. Den nuvarande arkitekturen i cellen, som innefattar titanoxid och Spiro-OMeTAD (en organisk förening) som laddningstransportlager (CTL), saknar stabilitet och visar hysteretiskt beteende. För att bedöma dessa stora problem utvecklas oorganiska CTL i PV-samhället. I detta arbete utförs en grundlig översyn av litteraturen om dessa oorganiska CTL. Fyra av dem identifieras som bra kandidater på grund av de höga prestanda de uppnådde och deras kemiska stabilitet: SnO2, ZnO, CuSCN och NiO. Betydelsen av gränssnitten i denna typ av cell visas också. Numerisk simulering av CTLs utförs också med ett dedikerat 1D-modelleringsverktyg (SCAPS), vilket gör att vi kan föreslå viktiga parametrar för att optimera i en CTL. Slutligen studeras effekterna av gränssnittet på prestanda hos en perovskit-solcell med hyperspektral avbildning av cellens fotoluminescensrespons. Med hjälp av en korrekt passningsalgoritm ger denna icke-destruktiva metod insikt om de opto-elektroniska egenskaperna hos perovskiten som odlas på olika substrat.
Perovskite solar cells are an emerging and promising thin film technology, which reached high efficiencies in an unprecedented short time. However, the current architecture of the cell, which includes titanium oxide and Spiro-OMeTAD (an organic compound) as charge transport layers (CTLs), lacks stability and shows hysteretic behavior. In order to assess these major issues, inorganic CTLs are developed in the PV community. This work performs a thorough review of the literature regarding these inorganic CTLs. Four of them are identified as good candidates because of the high performances they reached, and of their chemical stability: SnO2, ZnO, CuSCN and NiO. The significance of the interfaces in this kind of cell is also demonstrated.  Numerical simulation of CTLs is also performed using a dedicated 1D modelisation tool (SCAPS), which allows us to propose key parameters to optimize in a CTL. Finally, the effects of the interface on the performances of a perovskite solar cell are studied with hyperspectral imaging of photoluminescence response of the cell. Using a proper fit algorithm, this non-destructive method gives insight into the opto-electronic properties of the perovskite grown on different substrates.

Organische Solarzellen bieten die Aussicht auf eine ökologische und zugleich ökonomische Energiequelle. Nachteile des Konzepts liegen in der z.T. geringen Stabilität der für Absorption und Ladungstransport verwendeten Moleküle und einer unvollständigen Ausnutzung des Sonnenspektrums. Zur Verbesserung beider Merkmale werden in dieser Arbeit einzelne organische Bestandteile durch anorganische Materialien mit hoher Stabilität und breiten Absorptionsbanden ersetzt. Insbesondere werden als Absorber kolloidale Quantenpunkte (QP) verwendet, denen aufgrund nicht-linearer und durch Größeneffekte steuerbarer optischer Eigenschaften in der Photovoltaik der dritten Generation großes Interesse gilt. Dazu werden dünne anorganisch-organische Filme mit einem Verfahren hergestellt, das auf Wechselwirkungen zwischen Partikeln in Lösung und geladenen Oberflächen beruht (electrostatic layer-by-layer self-assembly). TiO2-Nanokristalle als Elektronenleiter, kolloidale CdTe- und CdSe-QP als Absorber und konjugierte Polymere als Lochleiter werden in die Filme integriert und diese als aktive Schichten in photovoltaischen Zellen verwendet. Die Struktur der Filme wird zunächst mittels AFM, SEM, XPS sowie durch eine Beladung mit organischen Farbstoffen untersucht. Sie weisen Porosität auf einer Skala von Nanometern sowie eine kontrollierbare Dicke und Mikrostruktur auf. Darauf aufbauend werden durch weitere lösungsbasierte Prozessschritte photovoltaische Zellen gefertigt und Zusammenhänge zwischen Struktur und Zellenleistung elektronisch und spektroskopisch untersucht. Einflussfaktoren der Zelleffizienz wie die Ladungsträgererzeugung und interne Widerstände können so bestimmt und die Effizienz von CdSe-QP als Sensibilisatoren nachgewiesen werden. Die Arbeit demonstriert die Eignung der gewählten Methoden und Zelldesigns zur Herstellung von photovoltaischen Zellen und eröffnet neue Ansätze für die Entwicklung und Fertigung insbesondere auf QP basierender Zellen.
Organic solar cells offer the prospect of a both ecological and economical energy source. Drawbacks of the concept are low stabilities of the molecules used for absorption and charge transport and an incomplete utilization of the solar spectrum. In order to improve both these characteristics, individual organic components are replaced by inorganic materials with a high stability and broad absorption bands in this work. In particular, colloidal quantum dots (QDs) are used as absorbers, the non-linear and size controllable optical properties of which are attracting great interest in third generation photovoltaics. For this application, inorganic/organic thin films are produced with a method based on interactions between particles in solution and charged surfaces (electrostatic layer-by-layer self-assembly). TiO2-nanocrystals as electron conductors, colloidal CdTe- and CdSe-QDs as absorbers and conjugated polymers as hole conductors are integrated into the films, which are used as active layers in photovoltaic cells. The structure of the films is investigated by AFM, SEM, XPS and by loading the films with organic dye molecules. The films show porosity on a nanometer scale as well as a controllable thickness and microstructure. Complemented by further solution based processing steps, photovoltaic cells are manufactured and correlations between the structure and performance of the cells are investigated both electronically and spectroscopically. Individual factors that determine the cell efficiency, such as carrier generation and internal resistances, are determined and the efficiency of CdSe-QDs as sensitizers is demonstrated. This work proves the suitability of the chosen methods and cell designs for manufacturing photovoltaic cells and opens up new approaches for the development and manufacture of in particular QD-based solar cells.

En esta tesis doctoral se han estudiado procesos fundamentales de reacciones de transferencia de carga en películas mesoporosas de dióxido de titanio sensitivizado con puntos cuánticos, en películas finas de mezclas polímero:puntos cuánticos y en dispositivos completos de mezclas del polímero PCPDTBT y puntos cuánticos de CdSe en operaciones de trabajo reales. Los resultados obtenidos permiten abordar la fabricación de dispositivos fotovoltaicos con un conocimiento de los procesos de recombinación que limitan la eficiencia de las celdas más amplio. Y por tanto, se demuestra la posibilidad de fabricar celdas solares basadas en puntos cuánticos con eficiencias iguales o superiores a los dispositivos fotovoltaicos orgánicos.
The fundamental processes of the charge transfer reactions between titania dioxide mesoporous films and quantum dots, in blend films of the semiconductor polymer P3HT and CdSe quantum dots and in complete devices fabricated with the polymer PDPCTBT and CdSe quantum dots in working conditions have been studied in this doctoral thesis. The obtained results allow the fabrication of photovoltaic devices with a deeper and wider knowledge of the recombination processes that limit the device efficiency. Therefore, it is demonstrated the possibility of fabrication of quantum dot based solar cells with efficiencies similar or higher than the organic photovoltaic devices.

Der Schwerpunkt der vorliegenden Arbeit liegt in der Charakterisierung der elektronischen Eigenschaften von hybriden organisch-anorganischen Perowskit (HOIP)-Schichten während der Schichtbildung und in verschiedenen Umgebungen mittels Photoelektronenspektroskopie (PES). Insbesondere wird der Methylammonium-Blei-Iodid-Chlorid-Perowskit (MAPbI3-xClx) untersucht. Als erstes werden Änderungen in den elektronischen Eigenschaften, der Zusammensetzung, sowie der Kristallstruktur mittels PES, Flugzeit-Sekundärionenmassenspektrometrie, sowie Röntgendiffraktometrie mit streifendem Einfall analysiert. Die Resultate weisen auf die entscheidende Rolle von Chlor im texturierten Wachstum der Perowskitschicht hin. Die auskristallisierte Perowskitschicht weist eine stärkere n-Typ Eigenschaft auf, welche auf die Änderung der Zusammensetzung während der Schichtbildung zurückgeführt werden kann. Außerdem beweisen die Ergebnisse eindeutig die Ablagerung von Chlor an der Grenzfläche zwischen der Perowskitschicht und dem Substrat. Zweitens werden die separaten Einflüsse von Wasser, Sauerstoff, und Umgebungsluft auf die elektronischen Eigenschaften von MAPbI3-xClx-Schichtoberflächen untersucht. Bereits geringste Wassermengen ähnlich wie im Hochvakuum oder in inerter Umgebung können eine reversible Reduzierung der Austrittsarbeit hervorrufen. Höherer Wasserdampf-Partialdruck führt zu einer Verschiebung des Valenzbandmaximums (VBM) weit vom Fermi-Niveau, sowie zu einer Reduzierung der Austrittsarbeit. Im Gegensatz dazu führt eine Sauerstoffexposition zu einer Verschiebung des VBM in Richtung des Fermi-Niveaus und zu einer Steigerung der Austrittsarbeit. Analog kommt es zu einer Verschiebung von bis zu 0.6 eV bei einer Exposition gegenüber Umgebungsluft, was den vorwiegenden Einfluss von Sauerstoff demonstriert. Die vorliegenden Untersuchungen betonen den kritischen Einfluss der Schichtbildung, der Zusammensetzung, sowie der Umgebungsbedingungen auf die elektronischen Eigenschaften von HOIP.
The present thesis aims at characterizing the electronic properties of solution-processed hybrid organic-inorganic perovskites (HOIPs) in general, and the HOIP methyl ammonium (MA) lead iodide-chloride (MAPbI3-xClx) films, in particular, at different stages, namely from its formation to its degradation, by means of photoelectron spectroscopy (PES). Firstly, the formation of MAPbI3-xClx films upon thermal annealing is monitored by a combination of PES, time-of-flight secondary ion mass spectrometry, and grazing incidence X-ray diffraction for disclosing changes in electronic properties, film composition, and crystal structure, respectively. Overall, the results point to the essential mediating role of chlorine in the formation of a highly textured perovskite film. The film formation is accompanied by a change of composition which leads to the film becoming more n-type. The accumulation of chlorine at the interface between perovskite and the underlying substrate is also unambiguously revealed. Secondly, the separate effects of water and oxygen on the electronic properties of MAPbI3-xClx film surfaces are investigated by PES. Already low water exposure – as encountered in high vacuum or inert conditions – appears to reversibly impact the work function of the film surfaces. Water vapor in the mbar range induces a shift of the valence band maximum (VBM) away from the Fermi level accompanied by a decrease of the work function. In contrast, oxygen leads to a VBM shift towards the Fermi level and a concomitant increase of the work function. The effect of oxygen is found to predominate in ambient air with an associated shift of the energy levels by up to 0.6 eV. Overall, the findings contribute to an improved understanding of the structure-property relationships of HOIPs and emphasize the impact of least variation in the environmental conditions on the reproducibility of the electronic properties of perovskite materials.

No estudo de sistemas híbridos orgânico-inorgânico, o uso de materiais como polímeros conjugados e óxidos de metal de transição tem despertado grande interes- se. Em particular, destacam-se sistemas compostos de tiofenos e óxido de titânio, que encontram uma importante aplicação em células solares. Para um melhor entendimento da interação entre os dois sistemas, torna-se necessário conhecer a organização do polímero sobre o substrato inorgânico. Desse modo, investigamos neste trabalho a formação da interface entre oligômeros de tiofeno e a superfície (101) de TiO2-anatase utilizando um enfoque de multiformalismo, que inclui simulações de dinâmica molecular clássica, e uma combinação de cálculos de primeiros princípios segundo Hartree-Fock e Teoria do Funcional da Densidade (DFT) para a determinação de propriedades estruturais e eletrônicas. A deposição de oligômeros de tiofeno sobre TiO2, constituindo sistemas de milhares de átomos, foi simulada por meio de dinâmica molecular clássica. Como requisito do cálculo clássico para estes sistemas, realizamos a reparametrização do campo de forças Universal tanto para os oligômeros, cujas estruturas não são bem descritas pelos campos de força padrões, como para o cristal e a superfície de TiO2. Foi observada a formação de filmes desordenados e densos de quatertiofeno, com a presença de uma maioria de moléculas de orientação quase perpendicular em relação ao plano superficial. Na camada de interface também se encontram moléculas dispostas paralelamente ao substrato, aumentando o contato entre os sistemas orgânico e inorgânico. A deposição de oligômeros isolados de quatertiofeno e de hexatiofeno mostra ainda que as moléculas se dispõem paralelas na superfície, alinhadas segundo direções de periodicidade dos átomos da superfície. Estudamos desta forma as propriedades eletrônicas de um sistema composto de politiofeno sobre TiO2, com o polímero paralelo na superfície e disposto na direção preferencial, através de um formalismo ab initio DFT. Apesar do tratamento DFT apresentar problemas conhecidos quanto na definição do gap, o que é mais relevante ainda no nosso caso de sistemas híbridos, os resultados revelam um deslocamento do topo da banda de valência do material orgânico em relação ao inorgânico. Isto possibilita o aprisionamento de um buraco no polímero, condição necessária para o uso deste tipo de sistema em células fotovoltaicas. Verifica-se ainda o acoplamento entre átomos de enxofre do politiofeno e de oxigênio do TiO2 através da presença de um estado associado a uma densidade eletrônica que se estende do polímero na superfície. Nossos resultados indicam assim um bom acoplamento eletrônico da superfície (101) de TiO2-anatase com politiofenos.
In the study of organic-inorganic hybrid systems, the use of materials such as conjugated polymers and transition metal oxides has attracted great interest. In particular, it is worth mentioning systems composed by thiophenes and titanium oxide, which have an important application in solar cells. For a better understand- ing of the interaction between these systems, it is necessary to know the polymer organization over the inorganic substrate. Therefore, we investigated in this work the formation of the interface between thiophene oligomers and the (101) surface of TiO2-anatase by means of a multi-formalism approach, which includes classical molecular dynamics simulations, and a combination of ¯rst principles calculations based on Hartree-Fock and Density Functional Theory (DFT) for structural and electronic properties. The simulation of deposition of thiophene oligomers on TiO2, which demands systems with thousands of atoms, was performed by classical molecular dynamics. As a prerequisite for the classical calculation for these systems, we performed a re-parameterization of the Universal force ¯eld for the oligomers, whose structures are not well described by standard force ¯elds, and for the TiO2 bulk and surface. We observed the formation of disordered and dense quaterthiophene ¯lms, with presence of a majority of molecules oriented almost perpendicularly to the surface plane. In the ¯rst interfacial layer we ¯nd also molecules oriented parallel to the sub- strate, which increases the contact between the organic and the inorganic systems. The deposition of isolated quaterthiophene and sexithiophene oligomers resulted in molecules disposed parallel to the surface and aligned along directions of periodicity of the surface atoms. We therefore studied the electronic properties of a system composed of poly- thiophene on TiO2, with the polymer parallel to the surface and oriented along a preferential direction, by means of DFT formalism. Although DFT treatments present known problems in the de¯nition of the energy gap, even of more relevance in our case of hybrid systems, the results for the occupied states revealed a sizeable displacement of the top of the valence band of one system with respect to the other. The misalignment will prevent the passage of a hole from the polymer to the oxide, providing in this way the necessary condition for the use of this type of system in solar cells. It was also seen electronic coupling between sulfur atoms from polythio- phene, and oxygen atoms from TiO2 through the presence of a state associated with an electronic density extended from the polymer to the surface. Our results thus indicate there is good electronic coupling between the (101) surface of TiO2-anatase and polythiophenes.

碩士
臺灣大學
物理研究所
98
At the time of energy crisis, it is urgent to find proper renewable energy. Among all the possibilities, solar cells are the most noticeable. There are many kinds of solar cells. Of all these solar cells, the crystalline based solar cells have the highest efficiency. But its production process is quite costly, lacking economical benefits. In contrast, organic solar cells have a great advantage of low cost. It only needs a spin coater to fabricate the active layer and then annealed with a hotplate. With its low cost and thin thickness, it would be practical to use them on plastic board to make flexible solar cells. This thesis is mainly focused on the research of inorganic/organic hybrid solar cells. The inorganic/organic hybrid solar cells are made from ZnO rods and polymer P3HT/PCBM. After cleaning the ITO glass, ZnO rods were fabricated by the hydrothermal method, and then P3HT/PCBM was spin coated on ZnO nanorods. Finally, Ag contact was evaporated for the measurement of photocurrent. We discover that a thin layer deposited by spin coated C60 solution before the fabrication of P3HT/PCBM layer can greatly improve the performance of solar cells. The main reasons for the increased efficiency of solar cells can be attributed to the enhanced exciton separation as well as the reduction of defect states. As a result, charges can transfer from polymer blend to ZnO-nanorod more effectively and subsequently travel to electrodes leading to the improved performance in the photovoltaic devices.

碩士
國立交通大學
光電工程研究所
102
We propose a series-connected hybrid tandem solar cell which consists of an organic solar cell (P3HT/PC60BM) as the top cell and an organic/crystalline silicon hybrid solar cell (PEDOT:PSS/c-Si nanowires) as the bottom cell. Based on the device structure, the organic materials can be directly spun-cast onto the inorganic silicon substrate with thermally evaporated metal contacts, making solution-based processes possible for rapid and low-cost production. With a proper design, the hybrid tandem device architecture can achieve a high open-circuit voltage (VOC) and power conversion efficiency (PCE), offering a promising approach for next-generation, low-cost and high-efficiency photovoltaics. We established a device simulation model to investigate the photovoltaic characteristics of the proposed hybrid tandem solar cells by combining the organic and silicon-based hybrid solar cells with a hypothetic recombination layer. First, the model of single junction solar cells is fitted to the current-voltage curve of fabricated devices. Next, we investigate the properties of the recombination layer between the sub-cells and observe strong correlations with the photovoltaic performance of tandem cells. In our preliminary model, we have realized a tandem cell with an open-circuit voltage (VOC), short-circuit current (JSC), fill-factor (FF) and power conversion efficiency (PCE) of 0.949 (V), 6.794 (mA/cm2), 57.743 % and 3.724 %, respectively. We also designed the structures and processes for the sub-cells and hybrid tandem solar cells fabrication. The intermediate layer between the sub-cells strongly affects the photovoltaic performance of the tandem cells and can be presented with evaporation or solution process. Currently, the characteristics of real hybrid tandem solar cells remain significantly lower than the simulation results. For evaporation process, we obtained the tandem cell with an open-circuit voltage (VOC), short-circuit current (JSC), fill-factor (FF) and power conversion efficiency (PCE) of 0.745 (V), 3.895 (mA/cm2), 40.561 % and 1.177 %, respectively. For solution process, we obtained the tandem cell with an open-circuit voltage (VOC), short-circuit current (JSC), fill-factor (FF) and power conversion efficiency (PCE) of 0.772 (V), 3.132 (mA/cm2), 23.957 % and 0.58 %, respectively. A number of challenging issues, including interface physics、recombination layer and device design will be discussed in this thesis.

碩士
國立交通大學
應用化學系分子科學碩博士班
102
Over the past few years, hybrid devices based on conjugated polymer/silicon heterojunction structures .In this paper, hybrid solar cell based on poly(3,4-ethylene- dioxythiophene):polystyrenesulfonate (PEDOT:PSS) directly spin-coating on n-type silicon wafer and n-type GaAs wafer. In the first part, a hybrid PEDOT:PSS/silicon heterojunction solar employed several n-type silicon substrate with different quality and thickness .Compared to the planar PEDOT:PSS/silicon cells,the maximal power conversion efficiency under AM 1.5 global one sun illumination is 9.76%. In the second part,A typical III–V solar cell requires a thickness of several micrometers to absorb all of the incoming photons. We present 3000-nm-thick GaAs absorbing layer based on heavily-doping GaAs grown by Molecular beam epitaxy ,coated with PEDOT:PSS. The highest power conversion efficiency under AM 1.5 global one sun illumination is 9.874%.

碩士
國立臺北科技大學
化學工程系碩士班
91
Solar light is the most important source of safe and regenerative energy because it is the only inexhaustible energy source. The main purpose of this paper describes as follows: First, inorganic nanoparticles (TiO2) and organic conducting polymer (MEH-PPV) was synthesized and manufactured the double layers solar cells. Second, the dye molecule (mercurochrome) was added to fabricate as an all solid-state dye-sensitized solar cells (DSSCs). The characteristic I-V curve of these solar cells will be discussed. The TiO2 nanoparticles was synthesized by sol-gel method method. SEM and TEM could decide the size of nanoparicles. The morphology of nanoparticles on the substrate could be observed by AFM. The crystal structure of TiO2 particles could be analyzed by XRD. According to the characteristic peak of XRD, we can calculate the size with Scherrer equation. NMR and FT-IR will be characterized the structure of MEH-PPV. The Mw and PDI of MEH-PPV were decided by GPC. The maximum absorption peak of MEH-PPV was measured by UV-Vis spectra and could be calculated the energy gap via the equation.

碩士
國立交通大學
光電工程學系
100
An organic/inorganic hybrid solar cells are cheap alternatives to conventional silicon-based solar cells. The devices take the advantages of high optical absorption and carrier mobility of inorganic semiconductors, while maintaining the easy processing attributes of polymers or other soft materials. However, the conduction of holes has been a major technical barrier for the advance of such novel devices. In this study, a hybrid PEDOT:PSS/silicon heterojunction solar cell is demonstrated with an average power conversion efficiency of 9.84% using rapid solution-based organic processes. Then we propose the use of silver nanowires (AgNWs) to improve the series resistance of the hybrid solar cells and further to realize solution-processed silicon-based photovoltaics. At last, the modeling of such devices predicts an efficiency exceeding 20% with improved reflection loss and material properties, shedding light into the attainment of high-efficiency and low-cost photovoltaics based on organic/inorganic hybrid devices. In the first section of my thesis, we discuss how to fabricate hybrid heterojunction solar cells with silicon nanowire and pyramidal surface textures. The hybrid heterojunction solar cells are demonstrated based on the composite of conductive polymer PEDOT:PSS directly spun-cast on a micro-textured n-type crystalline silicon wafer. Moreover, the industrial-standard microscale surface textures improve the antireflection and carrier collection without increasing much surface recombination. Then we replace the frontal metal contacts with the coating of AgNWs. The cross-linked AgNWs offer high transparency and low sheet resistance, which can be easily fabricated using low-cost and non-toxic materials. In the second section, we employed a self-consistent drift-diffusion and Poisson solver to theoretically investigate the effects of interface/bulk defects, doping concentration, and back surface recombination on the device performance. With a proper choice of band alignment, the modeling of such devices predicts an efficiency exceeding 20% with improved reflection loss and material properties.

博士
國立臺灣大學
材料科學與工程學研究所
97
This thesis aims to explore an alternative for silicon based solar cell. The hybrid materials, which are a combination of conjugated polymer and inorganic nanomaterial, provide numerous promising device properties such as effective carrier transport, strong light absorption and flexibility. Compared with conventional silicon based solar cell, this hybrid material can provide a low cost, environmental friendly, light weight and easy to process possibility. Though the performance of polymer based solar cell is still too low for large scale application, it is still possible to increase device conversion efficiency by improving carrier transport and extending light harvesting range. In chapter 3, we focus on studying organic-inorganic hybrid bulk heterojunction solar cell based on conjugated polymer P3HT and TiO2 nanocrystal. Our result show the optimal device performance can be achieved by introducing 50 weight percent TiO2 nanorod into P3HT matrix. By TiO2 surface modification, the optimal device performance has a power conversion efficiency of 2.2%. Compared with CdSe/conjugated polymer hybrid, this material system not only provides comparable device efficiency, but also develops a nontoxic, environmental friendly solar cell. In Chapter 4, we demonstrate enhanced the performance of polymer solar cell based on poly(3-hexylthiophene)(P3HT)/ZnO nanorods array heterojunction hybrid. By infiltrating P3HT polymer chain along ZnO nanorods array nanostructure, carrier mobility has been found a increase from 8.2×10-5 cm2/Vs to 7.7×10-4 cm2/Vs, companied with polymer chain were aligned perpendicularly to substrate surface. The optical anisotropic measurement revealed that chain orientation of P3HT prefers align along ZnO (l0Ī0) surface. Our experiments also showed that device performance can be further improved by surface modified ZnO nanorod surface. A novel approach to improve polymer solar cell using electric field assisting process was proposed in chapter 5. Our results showed better device performance can be achieved by carefully applied electric field during thin film process. Atomic force microscopy measurement showed higher polymer chain organization properties of blend film. By changing the natural orientation of polymer order, the electrical properties, including device performance, carrier mobility in vertical direction can both be enhanced. The optical anisotropic measurement also showed the optical anisotropic ratio is as a function of the magnitude of electric field. A solution process single wall carbon nanotube (SWCNT) thin film as a transparent electrode for organic solar cell application was studied in chapter 6. By chemical modified SWCNT thin films using nitric acid and thionyl chloride treatments, a significant decrease of sheet resistance can be achieved. Photovoltaic devices based on P3HT and PCBM fabricated on surface functionalized SWCNT electrode shows a promising device conversion efficiency of 1.87% can be performed. The variation of open circuit voltage (Voc) in P3HT and PCBM bulk heterojunction organic photovoltaic with functionalized transparent SWCNT networks indicated that the change of surface potential of SWCNT thin films resulted in correlated change in short circuit current density and open circuit voltage of the photovoltaic devices. In previous chapters, we have proposed several approaches to improve device performance. In chapter 7, we use new material for organic IR harvesting solar cells application based on P3HT/FeS2 blend. The devices exhibited high photo-electric current conversion efficiency in infrared region (>700 nm).where the external quantum efficiency was 6.5% at wavelength 650nm and 1% at 700 nm. The photoresponsed measurement also indicated that onset of photogenerated edge was about 900nm, which is contributed by FeS2 NCs. These results also pointed out that FeS2 NCs: P3HT hybrid can provide a low cost, environment friendly and easy process organic solar cell. Finally, polymer solar cells that have been constructed by hybrid materials are very promising. This thesis mainly studied polymer solar cells and has provided some approaches to improve device performance. Our findings showed carrier transport properties and excitons dynamics are both directly influenced by photoactive layer morphology. In the future, we believe device performance can be further improve by optimized morphology of polymer based heterojunction solar cell with a good percolation of both phases to the respective electrode.

Developing a fundamental understanding of photocurrent generation processes at organic-inorganic interfaces is critical for improving hybrid solar cell efficiency and stability. This dissertation explores processes at these interfaces by combining data from photovoltaic device performance tests with characterization experiments conducted directly on the device. The dissertation initially focuses on exploring how morphologically and chemically modifying the organic-inorganic interface, between poly(3-hexylthiophene) (P3HT) as the electron donating light absorbing polymer and titanium dioxide (TiO₂) as the electron acceptor, can result in stable and efficient hybrid solar cells. Given the heterogeneity which exists within bulk heterojunction devices, stable interfacial prototypes with well-defined interfaces between bilayers of TiO₂ and P3HT were developed, which demonstrate tunable efficiencies ranging from 0.01 to 1.6 %. Stability of these devices was improved by using Cu-based hole collecting electrodes. Efficiency values were tailored by changing TiO₂ morphology and by introducing sulfide layers like antimony trisulfide (Sb₂S₃) at the P3HT-TiO₂ interface. The simple bilayer device design developed in this dissertation provides an opportunity to study the precise role played by nanostructured TiO₂ surfaces and interfacial modifiers using a host of characterization techniques directly on a working device. Examples introduced in this dissertation include X-ray photoelectron spectroscopy (XPS) depth profiling analysis of metal-P3HT and P3HT-TiO₂ interfaces and Raman analysis of bonding between interface modifiers like Sb₂S₃ and P3HT. The incompatibility of TiO₂ with P3HT was significantly reduced by using P3HT derivatives with -COOH moieties at the extremity of a polymer chain. The role of functional groups like -COOH in interfacial charge separation phenomena was studied by comparing the photovoltaic behavior of these devices with those based on pristine P3HT. Finally, for hybrid solar cells discussed in this dissertation to become commercially viable, high temperature processing steps of the inorganic TiO₂ layer must be avoided. Accordingly, this dissertation demonstrates the novel use of electromagnetic radiation in the form of microwaves to catalyze growth of anatase TiO₂ thin films at temperatures as low as 150 °C, which is significantly lower than that used in conventional techniques. This low temperature process can be adapted to a variety of substrates and can produce patterned films. Accordingly, the ability to fabricate TiO₂ thin films by the microwave process at low temperatures is anticipated to have a significant impact in processing devices based on plastics.
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碩士
國立清華大學
材料科學工程學系
102
In this thesis, I focus on the fabrication and characterization of solution-processed small molecule organic solar cells (SMOSCs) and organic-inorganic hybrid solar cells. In the first chapter, I briefly review the development of modern photovoltaics including SMOSCs, polymer solar cells, silicon/organic organic-inorganic hybrid solar cells and perovskite solar cells. In the second chapter, the operation principles and characteristics of organic and organic-inorganic hybrid solar cells are described, followed by the details of device structures, materials analyses, device fabrications and characteristics measurements. In the third chapter of the thesis, a series of acceptor-acceptor-donor-acceptor-acceptor (A-A-D-A-A) symmetrical small molecules are studied as donor material for solution-processed SMOSCs. Various fabrication methods, device structures and acceptor materials are used to optimize the cell performance. Among all compounds, JW2 gives the highest power conversion efficiency (PCE) of 1.7 %, with an open circuit voltage (Voc) of 0.85 V, a short circuit current density (Jsc) of 5.26 mA/cm2, and a fill factor (F.F.) of 0.39. In the fourth chapter, we fabricate planar-type organic-inorganic hybrid solar cells based on single crystalline silicon covered by organic hole transporting material poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). A simple surface passivation method: Ultraviolet (UV)-ozone treatment is demonstrated. The effects of Si/PEDOT:PSS interfaces on device performances are further studied. In the second part of this chapter, the dielectric material-metal-dielectric material (DMD) structures as transparent electrodes are applied to the planar-type organic-inorganic solar cells. Finally, pyramid structures are tested and investigated under optical microscope and scanning electron microscope. In the fifth chapter of the thesis, blade-coated and spin-coated perovskite films are first fabricated. High efficiency solution-processed perovskite solar cells with an optimized annealing time and electron transporting layer thickness deliver a PCE of 11.7 %, with Voc of 0.87 V, a Jsc of 20.74 mA/cm2, a F.F. of 0.65. The PCE is further improved to 13.8 % by fine tuning of the material composition in the perovskite absorbing layers. In the last part of this section, several transporting layers are inserted into the device structures and Indium Tin Oxide (ITO)-free perovskite solar cells are successfully fabricated.

碩士
國立臺灣大學
光電工程學研究所
97
In this study, we focus on fabrications of organic polymer/Inorganic semiconductor hybrid solar cells. In the first part of the work, large-area GaAs nanowires are fabricated using SiO2 nanoparticles monolayer as the etching mask. SiO2 nanoparticles monolayer is spin-coated on the GaAs substrate. To obtain a uniform monolayer of SiO2 nanoparticles across the substrate, raised temperature, adequate solution concentration, and the substrate treated with a solvent for interface activation are required. With the monolayer of SiO2 nanoparticles as the etching mask, the GaAs substrate is etched by Induced-Coupled Plasma Reactive Ion Etcher to form GaAs nanowires with a high aspect ratio. The diameter and length of GaAs nanowires can be controlled by the size of SiO2 nanoparticles and etching time of ICP-RIE. Then, we transferred GaAs nanowires onto the glass substrate with the P3HT:PCBM. We combined GaAs nanowires with P3HT:PCBM to fabricate conjugated polymer-based organic solar cells. In the second part of the work, we used solution process to replace deposition to spin NiO layer on polymer. NiO layer acts as an interfacial electron-blocking layer/hole-transporting layer (EBL/HTL). Utilizing its higher LUMO (lowest unoccupied molecular orbital) could block electron leakage to anode to recombine with hole. The leakage current is reduced to improve the power conversion efficiency of inverted structure with organic polymer/ZnO semiconductor hybrid solar cells. Our investigations show that utilizing NiO as an interfacial layer increases the shunt resistance from 502 W-cm2 to 632 W-cm2 , the filling factor from 53 % to 59 % , and the power conversion efficiency from 3.3% to 3.8%. Besides, the stability in the air of cells with NiO film has good performance. After 60 days, the power conversion efficiency of the cell reaches constant with 2.91%.

碩士
國立臺灣大學
光電工程學研究所
96
Conjugated polymer-based organic solar cells have attracted considerable attention in recent years because they have many advantages, such as low-cost, processing with low temperature, flexible, large area production and so on. To increase the power conversion efficiency of organic solar cells, the most common strategy is so-called bulk heterojunction, in which donors such as poly(3-hexylthiophene) (P3HT) and acceptors like [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are blended to form one mixed layer. The bulk heterojunction devices were characterized by an interpenetrating network of donor and acceptor materials, providing a large interface area where photo-induced excitons could efficiently dissociate into separated electrons and holes. However, the interpenetrating network cannot be easily formed in the blended mixture. In addition, the organic materials are not good in carrier transport. Thus the power conversion efficiency is still limited by the low dissociation probability of excitons and the inefficient hopping carrier transport. Therefore, we combined single-crystalline Si nanowires with P3HT:PCBM to overcome the drawbacks of the conjugated polymer-based organic solar cells. The well-aligned SiNWs are fabricated from Si wafer and transferred onto the glass substrate with the P3HT:PCBM. Such SiNWs provide an uninterrupted conduction path for electron transport, enhance the optical absorption to serve as an interesting candidate of the absorber, and increase the surface area for exciton dissociation. Our investigations show that SiNWs are promising for hybrid organic photovoltaic cells with improved performance by increasing the short-circuit current density from 7.17 to 11.61 mA/cm2.

碩士
國立清華大學
電子工程研究所
94
Polymer solar cells exhibit many advantages such as the lightweight、processing feasibility and the potential to scale up to large area. Therefore polymer solar cells have been under intensive research. It usually contains single layer bulk heterojunction structure in the device. With large area for exciton separating, the efficiency of the device can be greatly improved. Recently, a better structure called ordered bulk heterojunction has been developed in dye-sensitized solar cells and molecular solar cells. It helps carriers transport and increases the efficiency of the device dramatically. In our study, we use P3HT conjugated polymer as hole transport material and 5nm×10nm CdSe inorganic colloidal nanorods as electron transport material. Blending two of them as the active layer, we form a bulk heterojunction film on the device with spin-coating. Under the illumination of monochromatic light with 532nm wavelength, the power conversion efficiency reaches 1%. In order to increase the carrier transport efficiency, we use single layer bulk heterojunction as basic structure and develop multilayer structure with spin-coating to achieve the similar effect of ordered bulk heterojunction. Using the sintering property of nanocrystals when annealed, we can create multilayer bulk heterojunction structure by slightly mixing the layers at the interface. In this study, we successfully developed blend/CdSe and blend(P3HT-rich)/blend ordered bulk heterojunction structures. Comparing to single layer bulk heterojunction, the series resistance decreases several times in ordered bulk heterojunction structure. It makes short circuit current and fill factor increase largely. The power conversion efficiency in blend/CdSe structure is 2.4% under the illumination of monochromatic light with 532nm wavelength. In blend(P3HT-rich)/blend structure, the efficiency even reaches 3.1%！

碩士
國立成功大學
航空太空工程學系碩博士班
98
In this thesis , we make some changes in the organic solar cell：First , we try to imprint some inorganic nano-materials into the active-layer . It helps organic solar cell to absorb the light of different wavelength and the nano-materials may improve the transmission . Second , the nanostructures increase the contact area and it may produce more Jsc . Third , to use two kinds of solar cells to produce the tandem solar cell . It can absorbe the light of different wavelength , increase the Voc and improve the power conversion efficiency . We imprint some inorganic nano-materials into the active-layer of organic solar cell . For example：silicon nano-wires , ZnSe nano-materials and CdS nano-materials . There are several parts of my researches：1. P3HT+TiO2 , we use P3HT and the sol-gel of TiO2 to make the device , but the power conversion efficiency is not high , 0.11% . 2. P3HT+silicon nano-wires , to nano-imprint the silicon nano-wires into P3HT thin film , but it’s not enough to improve the power conversion efficiency . 3. P3HT+PCBM+nano-materials：(1) To use P3HT and PCBM to make device . After we optimize the process , the power conversion efficiency IV is improved successfully , 3.666% . (2) To grow the silicon nano-wires with different diameters on the ITO film , and then we use the blended solution (P3HT+PCBM) to spin on it . The P3HT+PCBM thin film covers the silicon nano-wires . Finally , to thermal evaporate electrode by Al or Au . The Au electrode has good effect and the power conversion efficiency is 0.138% . In addition , when the diameter increases , silicon nano-wires may effect the transmission and the Jsc reduces . (3) To Imprint silicon nano-wires , ZnSe or CdS nano-materials into the P3HT+PCBM thin film and the power conversion efficiency is 2.247% , 2.632% and 3.184% , respectively . It’s important to let nano-materials be imprint into the active-layer . The number of the nano-materials in the active-layer effects the result . 4. Tandem solar cell , we try to produce the tandem solar cell by using silicon and polymer , but the organic solar cell doesn’t work and Voc doesn’t increase .

碩士
國立成功大學
航空太空工程學系碩博士班
98
In this study, polyol route were used to prepare copper indium sulfide (CuInS, CIS), copper indium selenium (CuInSe, CISe), zinc sulfide (ZnS) and zinc selenium (ZnSe) and other nanoparticles. Through the X-ray diffraction and other analysis to confirmed the material properties. Incorporation of polymer organic semiconductor compounds as the active layer of hybrid solar cells. In order to achieve the best performance of the hybrid solar cells, this could be done by the adjustment process in the film thickness and temperature, and various solvents and concentration ratio and other parameters. In the preparation of hybrid solar cells, the highest efficiency of the present is 0.01%. The main reasons cause low power conversion efficiency is due to polymer and nanoparticles have phase difference between interfaces. In addition to the above parameters can be adjusted. The study also aimed at the surface modification of the nanoparticles, and the ratio of nanoparticles synthesis. Make improvements in these directions, and hopes to further achieve higher efficiency of hybrid solar cells. Except interface issues, the bandgap of material to match also is an issue. Resulting in the efficiency of device is still much room for improvement.

碩士
國立清華大學
電子工程研究所
94
Organic Solar Cells fabricated by conjugated polymer using solution-based processes are light-weighted, cost-effective in manufacturing and scalable to large-area devices. Due to the low electron mobility of conjugated polymer, it is believed that using materials which can efficiently transport electron may enhance the performance of the solar cells. We fabricate the active layer of solar cells by using blends of P3HT and colloidal CdSe nanorods. Colloidal nanorods are soluble in organic solvent and are able to provide a direct route for electron transport due to their anisotropic shape. Active layer spin coated by blend forms bulk heterojunction, which provide a large area of interface between P3HT and CdSe for charge separation. Efficient charge separation occurs at the interface of polymer and inorganic nanocrystals due to the heterojuntion structure, the short-circuit current of blend is 100 times larger than P3HT single layer. We successfully fabricate basic solar cell devices, and study the effects of processing steps. We find that surfactant exchange of CdSe nanorods is critical for charge separation and using mixed solvent will prevent nanorods from aggregation. The use of heat treatment and high-boiling-point solvent for blend enhances the performance of solar cells, which is tentatively attributed to more orderly arrangement of the polymer under these processing steps.

碩士
國立虎尾科技大學
光電與材料科技研究所
99
Polymer solar cells (PSCs) are fabricated using a novel film deposition method, the electrostatic spray (e-spray) technique. Stable atomization and uniform deposition of the polymer blend by e-spray are achieved by manipulating the solution concentration, the solvent composition, and the electric field. The performance of PSCs is primarily influenced by the inherent film morphology of the e-sprayed polymer-blend active layers, which is significantly different from that of the conventional films that are formed using the spin-coating (SC) method. In addition, the properties of organic/inorganic poly(3-hexylthiophene) (P3HT):TiO2 nanocomposite films and nanocomposite based solar cells as a function of TiO2 concentration and the solvent used for the film fabrication were studied. For low nanoparticle concentration (20–30%) the device performance was worse compared to pure P3HT, while for nanoparticle concentration of 40% significant improvements were obtained. On the other hand, poly (3-hexylthiophene) (P3HT): TiO2 nanocomposite films cost less time than poly (3-hexylthiophene) (P3HT): [6,6]-phenyl-C61 -butyric acid methyl ester (PCBM) films.

碩士
國立臺灣大學
電子工程學研究所
98
Organic photovoltaic devices are very attractive for their advantages of flexibility, light-weight, and large-area production at a dramatically low cost. In this study, the PV2000 material is used as a photoactive layer, which has a larger relative energy difference between the HOMO level of the electron-donating polymer and the LUMO level of the electron acceptor (energy difference ~1.7 eV) as compared to the standard P3HT:PCBM system, thereby leading to a larger VOC. The better contact in the interface is achieved by the post-annealing process, which corrects the defects between electrode and polymer layer interface. Moreover, the thermally induced morphology modification, crystallization and improved interfacial transportation, thereby leading to better charge collection and reduced series resistance. These results show that the process of post-annealing is very important for our PV2000 inverted device. We used solution process to replace deposition to spin NiO layer on active layer. NiO layer acts as an interfacial electron-blocking layer/hole-transporting layer (EBL/HTL). Utilizing its higher LUMO (lowest unoccupied molecular orbital) could block electron leakage to anode to recombine with hole. The leakage current is reduced to improve the power conversion efficiency of inverted structure devices. When the TiO2 nanorods are introduced, an improvement of light harvest and photocurrent is achieved due to several factors. First, the photoactive layer is thickened and the light path is increased to have more light absorption. Second, the morphology is modified to provide the photoactive layer and inorganic layer a larger contact area for efficient charge collection. Third, the TiO2 nanorods enhance the photoluminescence quenching, indicating improved electron-hole dissociation. In this way, the high PCE of 5.61% from inverted PSCs is achieved. In the second part of this work, our investigation apply the low band gap material (ITRI P47:PC70BM) as the photoactive layer. The light harvest is improved by adjusting the thickness of photoactive layer. In addition, we introduce the solution-process NiO layer between photoactive layer and silver as an electron blocking layer, therefore, the electron is forced to move toward the ITO electrodes, increasing the selectivity of the charge carriers and the shunt resistance of the photovoltaic cell.

The widespread adoption of hybrid organic-inorganic solar cells has been delayed by low performance. Improving performance requires a firm understanding of how to optimize both material composition and processing parameters. In this thesis, we examine processing parameters that include solution composition, annealing temperature, and the rates of spin casting and evaporative coating. We also find that the optimal weight ratio for the active layer of a ZnO:P3HT solar cell is 40 wt. % ZnO.
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碩士
國立臺灣大學
材料科學與工程學研究所
97
This work presents the study of surface modification of TiO2 nanorod in bulk heterojunction composites based on poly(3-hexylthiophene) (P3HT) and TiO2 nanorods, trying to improve the performance of organic/inorganic hybrid solar cells. Surface modification of TiO2 was performed by replacing the insulating surface ligand (oleic acid) with two kinds of conductive, novel interface modifiers: the derivative of copper phthalocyanine (Cudye) and the regioregular 3-hexylthiophene oligomer with carboxylic end functional groups (oligomer 3HT–COOH). As surface modification was carried out, the hybrid system exhibited an improved charge separation by showing a more pronounced PL quenching. Also, back recombination between electrons and holes can be suppressed from the transient photo-voltage measurement, revealing a longer charge carrier lifetime. Furthermore, the compatibility between P3HT and TiO2 can also be improved after surface modification, as P3HT and modified TiO2 exhibited a more similar surface hydrophobicity (by contact angle measurement) and higher polymer crystallinity in the hybrid films (by XRD). All the data show that the oligomer 3HT-COOH is the better performed interface modifier than Cudye. By clarifying the functions and roles of interface modifier in the active layer of photovoltaic devices, this study provides a possible route for increasing the efficiency of organic solar cells.

碩士
國立清華大學
光電工程研究所
102
This paper proposed a low temperature, solution process, simple process, a large area of the lead halide perovskite organic/inorganic hybrid solar cell. In this paper, in which the use of lead halide perovskite as the photoactive layer. With the high solubility PbCl2 in DMSO to increase the concentration of the precursor solution, and construct organic / inorganic hybrid solar cell. Our device configuration:Glass/ITO/PEDOT:PSS/Perovskite/PCBM/Al belong to normal structure. Suitably selected the hole and the electron transport layer by spin coating and dried to optimize conditions for the performance of the solar cell of the present paper is better. In this paper, Construction of the solar cell efficiency of up to 7.0 %, short-circuit current of 18.1 mA/cm2 has excellent performance. Lead halide perovskite organic / inorganic hybrid solar cell laden with good efficiency and performance advantages of a large area can be to facilitate the production of large-area components toward future development.

碩士
國立交通大學
光電工程研究所
103
In this thesis, we successfully use tubular copper foil to grow high-quality single-crystalline graphene. In order to scale up for device applications, we have further optimized and improved the growth parameters. First, we use graphite as blockers to increase the probability of gas collisions on to the copper foil. We obtain high-quality graphene but the uniformity is not as ideal. Next, we prepare an oxide layer on the copper foil with surface cleaning techniques, which successfully increase the grain size of graphene to about tens of microns. Finally, we change the growth time and gas flow rate, where low rate and long growth time result in high-quality graphene of which the ratio of Raman signal 2D/G peak is 3 with very good uniformity. Moreover, we transfer this high-quality graphene onto a PET film as the transparent conductive electrode for hybrid organic-inorganic solar cells. According to the simulation, we can see that later carrier conduction of PEDOT:PSS is limited by the doping concentration as well as the conductivity. Therefore, we have employed graphene transparent conductive film to help collect and transport carriers. In the silicon base hybrid solar cells, the two-layer-graphene transparent conductive film give rise to the best device performance. The power conversion efficiency of device is 8.95 %, corresponding to an enhancement factor of 53.5%. In the GaAs base hybrid solar cells, we use single-layer- graphene transparent conductive film to optimize the cells. The power conversion efficiency of device is 8.60 %, corresponding to enhancement of 25.5%.

碩士
國立臺灣大學
應用物理所
99
A new flexible organic/inorganic hybrid photovoltaic (HPV) device has been demonstrated. The layered structure of the HPV consists of polyethylene terephthalate (PET)/ Graphene /ZnO nanorods/ poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM)/Ag. It is found that the power conversion efficiency and the short-circuit current density of the device can be enhanced with increasing bending angles. The highest enhancement of power conversion efficiency can reach up to 30% compared with flat counterpart. While the device returns to the original condition, the power conversion efficiency will recover to its initial value. These interesting phenomena can be attributed to the light trapping effect in ZnO nanorods and the outstanding capability of graphene.