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Lin, Keng-Chu. "NOVEL TITANIA NANOSTRUCTURES FOR PHOTOVOLTAIC APPLICATIONS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1372856925.
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Mohseni, Kiasari Nima. "ZnO nanostructures for sensing and photovoltaic devices." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46367.
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In this PhD thesis, vertical arrays of zinc oxide (ZnO) nanowires (NWs) are synthesized in a CVD system and then deposited on patterned electrodes using dielectrophoresis (DEP). The nanowire devices illustrate 4 orders of magnitude increase in conductivity when exposed to ultra violet (UV) irradiation of 1220 μW/cm². The UV response has a fast component, due to electron-hole generation, as well as a slower component, attributed to the release of oxygen. Moreover, due to the increased electron density in the presence of UV, the type of oxygen species on the surface of ZnO changes to more reactive negative ions. In addition, when the pressure is decreased to 0.05 mBar, the conductivity of the NWs increases ∼ 2 and 3.5 times for NWs with 300-nm and 100-nm diameter, respectively. For the first time, UV irradiation is used to improve the carbon monoxide (CO) sensing properties of ZnO. When exposed to 250 μW/cm² UV irradiation, not only the sensitivity increases more than 75%, but also a repeatable and recoverable response is obtained, which is due to formation of more reactive oxygen ions. For the same reason, when the temperature is elevated, higher sensitivity to CO is achieved. The devices demonstrate exponential sensitivities of more than 5 decades to 60% increase in relative humidity (RH) at room temperature, which is a record for ZnO NW based RH sensors.
A novel, low-cost and simple technique is developed for fabrication of sensors based on solution processed ZnO nanoparticles (NPs) by simply sketching the electrode lines and painting the NP ink. Sensors show 2000 times increase in conductivity when exposed to 1220 μW/cm² UV irradiation and more than 200% increase in current when exposed to 5-mins of CO pulse at room temperature.
Furthermore, this thesis presents efficient (3.8%) inverted organic photovoltaic devices based on a P3HT:PCBM bulk heterojunction blend with improved charge-selective layers. ZnO NP films with different thicknesses are deposited on the transparent electrodes as a nano-porous electron-selective contact layer. The optimized inverted devices show exceptional short circuit current, which is related to increased quantum efficiency.
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Lim, Swee Hoe. "Metallic nanostructures for optoelectronic and photovoltaic applications." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3365871.
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Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed August 20, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Kulakci, Mustafa. "Silicon Nanostructures For Electro-optical And Photovoltaic Applications." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614225/index.pdf.
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Recently extensive efforts have been spent in order to achieve all silicon based photonic devices exploiting the efficient light emission from nanostructured silicon systems. In this thesis, silicon based nanostructures have been investigated for electro-optical and photovoltaic applications. The thesis focused on three application areas of silicon nanostructures: Light emitting diode (LED), light modulation using quantum confined Stark effect (QCSE) and photovoltaic applications.
In the context of LED applications, ZnO nanocrystal/silicon heterojunctions were investigated. Contrary to observation of pure ultraviolet photoluminescence (PL) from ZnO nanocrystals that were synthesized through vapor liquid solidification (VLS) method, visible emissions were observed in the electroluminescence (EL) due to defect states of ZnO. The discrepancy between these emissions could be ascribed to both change in excitation mechanisms and the defect formation on ZnO nanocrystals surface during device fabrication steps. EL properties of silicon nanocrystals embedded in SiO2 matrix were also systematically studied with and without Tb doping. Turn-on voltage of the Tb doped LED structures was reduced below 10 V for the first time.
Clear observation of QCSE has been demonstrated for the first time in Si nanocrystals embedded in SiO2 through systematic PL measurements under external electric field. Temperature and size dependence of QCSE measurements were consistently supported by our theoretical calculations using linear combination of bulk Bloch bands (LCBB) as the expansion basis. We have managed to modulate the exciton energy as high as 80 meV with field strength below MV/cm. Our study could be a starting point for fabrication of electro-optical modulators in futures for all silicon based photonic applications.
In the last part of the thesis, formation kinetics of silicon nanowires arrays using a solution based novel technique called as metal assisted etching (MAE) has been systematically studied over large area silicon wafers. In parametric studies good control over nanowire formation was provided. Silicon nanowires were tested as an antireflective layer for industrial size solar cell applications. It was shown that with further improvements in surface passivation and contact formation, silicon nanowires could be utilized in very efficient silicon solar cells.
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Dorval, Courchesne Noémie-Manuelle. "Biologically-templated metal oxide and metal nanostructures for photovoltaic applications." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98705.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.Cataloged from PDF version of thesis. Vita. Page 296 blank.
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In several electronic, electrochemical and photonic systems, the organization of materials at the nanoscale is critical. Specifically, in nanostructured heterojunction solar cells, active materials with high surface area and continuous shapes tend to improve charge transport and collection, and to minimize recombination. Organizing nanoparticles, quantum dots or organic molecules intro three-dimensional structures can thus improve device efficiency. To do so, biotemplates with a wide variety of shapes and length scales can be used to nucleate nanoparticles and to organize them into complex structures. In this work, we have used microorganisms as templates to assemble metal oxide and metal nano- and microstructures that can enhance the performance of photovoltaic devices. First, we used M13 bacteriophages for their high aspect ratio and ability to bind noble metal nanoparticles, to create plasmonic nanowire arrays. We developed a novel process to assemble bacteriophages into nanoporous thin films via layer-by-layer assembly, and we mineralized the structure with titania. The resulting porous titania network was infiltrated with lead sulfide quantum dots to construct functional solar cells. We then used this system as a platform to study the effects of morphology and plasmonics on device performance, and observed significant improvements in photocurrent for devices containing bacteriophages. Next, we developed a process to magnesiothermally reduce biotemplated and solution-processed metal oxide structures into useful metallic materials that cannot be otherwise synthesized in solution. We applied the process to the synthesis of silicon nanostructures for use as semiconductors or photoactive materials. As starting materials, we obtained diatomaceous earth, a natural source of biotemplated silica, and we also mineralized M13 bacteriophages with silica to produce porous nanonetworks, and Spirulina major, a spiral-shaped algae, to produce micro-coils. We successfully reduced all silica structures to nanocrystalline silicon while preserving their shape. Overall, this work provides insights into incorporating biological materials in energy-related devices, doping materials to create semiconductors, characterizing their morphology and composition, and measuring their performance. The versatility and simplicity of the bottom-up assembly processes described here could contribute to the production of more accessible and inexpensive nanostructured energy conversion devices.
by Noémie-Manuelle Dorval Courchesne.
Ph. D.
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Khoury, Rasha. "Nanometer scale point contacting techniques for silicon Photovoltaic devices." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX070/document.
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Au cours de cette thèse, j’ai étudié la possibilité et les avantages d’utiliser des contacts nanométriques au-dessous de 1 µm. Des simulations analytiques et numériques ont montré que ces contacts nanométriques sont avantageux pour les cellules en silicium cristallin comme ils peuvent entrainer une résistance ohmique négligeable. Mon travail expérimental était focalisé sur le développement de ces contacts en utilisant des nanoparticules de polystyrène comme un masque. En utilisant la technique de floating transfert pour déposer les nanosphères, une monocouche dense de nanoparticules s’est formée. Cela nécessite une gravure par plasma de O2 afin de réduire la zone de couverture des NPs. Cette gravure était faite et étudiée en utilisant la technique de plasmas matriciels distribués à résonance cyclotronique électronique (MD-ECR). Une variété de techniques de créations de trous nanométriques était développée et testée dans des structures de couches minces et silicium cristallin. Des trous nanométriques étaient formés dans la couche de passivation, de SiO2 thermique, du silicium cristallin pour former des contacts nanométriques dopés. Un dopage local de bore était fait, à travers ces trous nanométriques par diffusion thermique et implantation ionique. En faisant la diffusion, le dopage local était observé par CP-AFM en mesurant des courbes de courant-tension à l’intérieur et à l’extérieur des zones dopées et en détectant des cellules solaires nanométriques. Par contre le processus de dopage local par implantation ionique a besoin d’être améliorer afin d’obtenir un résultat similaire à celui de diffusionThe use of point contacts has made the Passivated Emitter and Rear Cell design one of the most efficient monocrystalline-silicon photovoltaic cell designs in production. The main feature of such solar cell is that the rear surface is partially contacted by periodic openings in a dielectric film that provides surface passivation. However, a trade-off between ohmic losses and surface recombination is found. Due to the technology used to locally open the contacts in the passivation layer, the distance between neighboring contacts is on the order of hundreds of microns, introducing a significant series resistance.In this work, I explore the possibility and potential advantages of using nanoscale contact openings with a pitch between 300 nm to 10 µm. Analytic and numerical simulations done during the course of this thesis have shown that such nanoscale contacts would result in negligible ohmic losses while still keeping the surface recombination velocity Seff,rear at an acceptable level, as long as the recombination velocity at the contact (Scont) is in the range from 103-105 cm/s. To achieve such contacts in a potentially cost-reducing way, my experimental work has focused on the use of polystyrene nanospheres as a sacrificial mask.The thesis is therefore divided into three sections. The first section develops and explores processes to enable the formation of such contacts using various nanosphere dispersion, thin-film deposition, and layer etching processes. The second section describes a test device using a thin-film amorphous silicon NIP diode to explore the electrical properties of the point contacts. Finally, the third section considers the application of such point contacts on crystalline silicon by exploring localized doping through the nanoholes formed.In the first section, I have explored using polystyrene nanoparticles (NPs) as a patterning mask. The first two tested NPs deposition techniques (spray-coating, spin-coating) give poorly controlled distributions of nanospheres on the surface, but with very low values of coverage. The third tested NPs deposition technique (floating transfer technique) provided a closely-packed monolayer of NPs on the surface; this process was more repeatable but necessitated an additional O2 plasma step to reduce the coverage area of the sphere. This was performed using matrix distributed electron cyclotron resonance (MD-ECR) in order to etch the NPs by performing a detailed study.The NPs have been used in two ways; by using them as a direct deposition mask or by depositing a secondary etching mask layer on top of them.In the second section of this thesis, I have tested the nanoholes as electrical point-contacts in thin-film a-Si:H devices. For low-diffusion length technologies such as thin-film silicon, the distance between contacts must be in the order of few hundred nanometers. Using spin coated 100 nm NPs of polystyrene as a sacrificial deposition mask, I could form randomly spaced contacts with an average spacing of a few hundred nanometers. A set of NIP a-Si:H solar cells, using RF-PECVD, have been deposited on the back reflector substrates formed with metallic layers covered with dielectrics having nanoholes. Their electrical characteristics were compared to the same cells done with and without a complete dielectric layer. These structures allowed me to verify that good electrical contact through the nanoholes was possible, but no enhanced performance was observed.In the third section of this thesis, I investigate the use of such nanoholes in crystalline silicon technology by the formation of passivated contacts through the nanoholes. Boron doping by both thermal diffusion and ion implantation techniques were investigated. A thermally grown oxide layer with holes was used as the doping barrier. These samples were characterized, after removing the oxide layer, by secondary electron microscopy (SEM) and conductive probe atomic force microscopy (CP-AFM)
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Prevost, Richard M. III. "Design and Fabrication of Nanostructures for the Enhancement of Photovoltaic Devices." ScholarWorks@UNO, 2017. http://scholarworks.uno.edu/td/2353.
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In 2012 the net world electricity generation was 21.56 trillion kilowatt hours. Photovoltaics only accounted for only 0.1 trillion kilowatt hours, less than 1 % of the total power. Recently there has been a push to convert more energy production to renewable sources. In recent years a great deal of interest has been shown for dye sensitized solar cells. These devices use inexpensive materials and have reported efficiencies approaching 12% in the lab. Here methods have been studied to improve upon these, and other, devices. Different approaches for the addition of gold nanoparticles to TiO2 films were studied. These additions acted as plasmonic and light scattering enhancements to reported dye sensitized devices. These nanoparticle enhancements generated a 10% efficiency in device performance for dye sensitized devices. Quantum dot (QD) sensitized solar cells were prepared by successive ionic layer adsorption and reaction (SILAR) synthesis of QDs in mesoporous films as well as the chemical attachment of colloidal quantum dots using 3-mercaptopropionic acid (3-MPA). Methods of synthesizing a copper sulfide (Cu2S) counter electrode were investigated to improve the device performance. By using a mesoporous film of indium tin oxide nanoparticles as a substrate for SILAR growth of Cu2S catalyst, an increase in device performance was seen over that of devices using platinum. These devices did suffer from construction drawbacks. This lead to the development of 3D nanostructures for use in Schottky photovoltaics. These high surface area devices were designed to overcome the recombination problems of thin film Schottky devices. The need to deposit a transparent top electrode limited the success of these devices, but did lead to the development of highly ordered metal nanotube arrays. To further explore these nanostructures depleted heterojunction devices were produced. Along with these devices a new approach to depositing lead sulfide quantum dots was developed. This electrophoretic deposition technique uses an applied electric field to deposit nanoparticles onto a substrate. This creates the possibility for a low waste method for depositing nanocrystals onto nanostructured substrates.
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Cheminal, Alexandre. "Ultrafast energy conversion processes in photosensitive proteins and organic nanostructures for photovoltaic applications." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE012/document.
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Les techniques de spectroscopie femtoseconde permettent d’étudier les processus de conversion d’énergie dans les système organiques. Elles permettent d’étudier les populations photo-générées et leur évolution à l’échelle de ces photoréactions. Elles permettent de comprendre les transferts d’énergie et de charge intra- et inter-moléculaires à l’origine du fonctionnement de ces systèmes.La protéine de rétinal Anabaena sensroy Rhodopsin est un photocommutateur naturel, qui est étudié afin de comprendre les paramètres à l’origine de l’efficacité quantique d’isomérisation. Nous avons pu déterminer cette efficacité quantique pour les deux formes stables du rétinal ainsi que leur dynamique d’isomérisation dans les mêmes conditions expérimentales.La génération de charge dans des couches actives pour le photovoltaique organique est étudiée dans un système composé d’un mélange de PCBM et d’un donneur organique dérivé du colorant BODIPY. L’influence de la nanostructuration de la couche active sur la génération de charge est étudiée. La génération de charge est limitée dans ce système par la recombinaison des charges générées et par la diffusion des excition aux interfaces donneur-accepteur. Ces observations indiquent que l’amélioration de la nanostructuration de la couche active peut permettre d’augmenter les rendements de photo-génération de chargeFemtosecond transient spectroscopies are used to investigate photonic energy conversion inorganic systems. These techniques allow to observe the ground and excited states of themolecules at the timescale of the photoreactions. It is used to understand the inter- andintramolecular energy and charge transfers leading to the desired photochemical process.The natural photoswiching retinal protein Anabaena sensory Rhodopsin is studied to understand the key parameters ruling the isomerisation quantum yield. We could determine the isomerisation quantum yield of both stable forms and their dynamics in the very same experimental conditions.Charge generation is investigated in small molecule bulk heterojunction active layers for organic solar cells made of PCBM and a BODIPY dye-derivative donor. The influence of the active layer morphology on charge generation is studied. The charge generation is limited by charge recombination but also by exciton diffusion to the donor-acceptor interface. The active layer morphology has to be improved to achieve more efficient organic solar cells with these materials
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Aguinaldo, Ryan. "Modeling solutions and simulations for advanced III-V photovoltaics based on nanostructures /." Online version of thesis, 2008. http://hdl.handle.net/1850/7912.
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Turner, Carrina Jayne. "Electrochemical deposition, characterisation and photovoltaic application of undoped and aluminium doped zinc oxide nanostructures." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/7122.
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Zinc oxide (ZnO) is an n-type II-VI semiconductor with a reported band gap of 3.2-3.6 eV [1, 2, 3] and electrical resistivity of ~ 50 Ωcm [4]. Ideal for use in devices such as Photovoltaics (PVs), Light Emitting Diodes (LEDs) and detectors, ZnO has the advantage that it can be electrochemically deposited. This enables the quick and cheap controlled growth of ZnO nanostructures, which can potentially enhance performance in electronic applications over thin films. ZnO doping with a group III element e.g. Aluminium, can increase ZnO conduction by several orders of magnitude whilst having only a subtle effect on its optical properties, therefore further enhancing device performance. For the first time, this thesis presents a unique in-depth study into the potentiostatic electrochemical deposition of well defined zinc oxide nanostructures (nanorods and platelets), their controlled aluminium doping and application in PV devices. This work addresses the mechanism of doping and examines the relationship between the opto-electronic properties, composition, structure, morphology and growth. The results show that arrays of crystalline wurtzite ZnO nanorods with strong (002) preferential orientation can be deposited on ITO and Au using a 1 mM Zn(NO3)2 system. Doping has been successfully carried out using Al(NO3)3 with a doping mechanism confirmed for the first time. This study shows that doped nanorods contain < 5 at. % Al3+, where Al3+ is incorporated in the ZnO lattice as interstitial and/or substitutional ions. This results in a subtle increase in the band gap, and is believed to increase the ZnO conduction by several orders of magnitude. The application of these nanorod arrays in PV devices has improved device efficiency by ~ 1080 %. Furthermore, platelets have been successfully deposited using a 5 mM Zn(NO3)2 system. A critical dopant content ~ 5 at. % Al3+ has been found, above which there is a transition in the doping mechanism towards spontaneous Al2O3 formation in addition to interstitial and substitutional Al3+ ion locations. This results in a gradual decrease in the optical band gap towards that of undoped ZnO. This mechanism occurs in platelets, where at. % Al3+ > 5 %. Platelet formation is associated with small quantities of impurities such as Al2O3, ZnCl2, Zn(ClO4)2 Zn5(OH)8Cl2.H2O and Au3Zn, arising from deposition conditions. Both impurities and dopants result in increased ZnO polycrystallinity and decreased ZnO (002) preferential orientation. The performance of PV devices with nanorod arrays has been shown to be better than previously reported equivalent thin film devices. This work illustrates the significance of electrochemical deposition as a technique for cheap and quick, controlled mass production of high quality tailor-made ZnO semiconductor nanostructures.
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Masuda, Koji. "Design and Fabrication of Nanostructures by Layer-by-Layer Assembly for Organic Photovoltaic Devices." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/123342.
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González, Valls Irene. "Vertically-aligned ZnO Nanostructures for excitonic Solar Cells." Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/121584.
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L’energia solar transforma la llum del Sol en electricitat i és una de les energies renovables més encoratjadores: no produeix CO2 i és una energía de baix cost alternativa a les fonts fòssils. Entre els diferents dispositius fotovoltaics, els de tercera generació, excitonic solar cells (XSCs), entre els quals inclouen: orgànic, híbrid i dye-sensitized solar cells, són prometedors per aconseguir els tres principals criteris per la seva comercialització: alta eficiencia, baix cost i la possibilitat de ser fabricats amb mètodes simples i escalables.
L’aplicació de ZnO en XSCs s’ha incrementat en els últims anys degut a les seves similaritats amb l’ òxid semiconductor més utilitzat i estudiat, el TiO2. El ZnO presenta un valor de band gap i la banda de conducció similars i també és més alta la mobilitat dels electrons comparat amb el TiO2. Es pot sintetitzar de moltes formes diferents amb tècniques senzilles i escalables. I en concret, l’aplicació de nanoestructures verticals de ZnO s’ha estudiat per millorar el contacte entre els materials donador i acceptor d’electrons en cel·les solar orgàniques (OSCs), o millorar la injecció d’electrons en cel·les solars Dye-sensitized (DSCs).
El treball d’aquesta tesis s ’enfoca en la preparació i caracterització de nanostructures de ZnO: nanorods (NR), nanotrees (NTr) i core-shells (CS) i la seva aplicación en DSCs i OSCs. L’optimització de tots els paràmetres de les cel·les solars per millorar l’eficiència també es presenta en aquest treball.Solar energy converts the sunlight into electricity and is one of the most encouraging renewable, CO2-free and low cost alternative energy source to fossil fuels. Among the different photovoltaic devices the third-generation excitonic solar cells (XSCs), which include organic, hybrid and dye-sensitized solar cells, are promising devices for the achievement of the three main criteria that would lead to large scale commercialization: high efficiency, low cost and the possibility to apply simple and scalable fabrication techniques. The application of ZnO in XSCs has been rising over the last few years due to its similarities with the most studied semiconductor oxide, TiO2. ZnO presents comparable band gap values and conduction band position as well as higher electron mobility than TiO2. It can be synthesized in a wide variety of nanoforms applying straight forward and scalable synthesis methodologies. Specially, the application of vertically-aligned ZnO nanostructures it is thought to improve contact between the donor and acceptor material in organic solar cells (OSC), or improve electron injection in Dye sensitized solar cells (DSCs). The present thesis focuses on the preparation and characterization of ZnO nanostructures: nanorods (NR), nanotrees (NTr) and core-shells (CS) and their application in DSCs and OSCs. The optimization of the solar cell parameters to enhance its performance is also presented here.
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Saliba, Michael. "Plasmonic nanostructures and film crystallization in perovskite solar cells." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:fdb36a9e-ddf5-4d27-a8dc-23fffe32a2c5.
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The aim of this thesis is to develop a deeper understanding and the technology in the nascent field of solid-state organic-inorganic perovskite solar cells. In recent years, perovskite materials have emerged as a low-cost, thin-film technology with efficiencies exceeding 16% challenging the quasi-paradigm that high efficiency photovoltaics must come at high costs. This thesis investigates perovskite solar cells in more detail with a focus on incorporating plasmonic nanostructures and perovskite film formation. Chapter 1 motivates the present work further followed by Chapter 2 which offers a brief background for solar cell fabrication and characterisation, perovskites in general, perovskite solar cells in specific, and plasmonics. Chapter 3 presents the field of plasmonics including simulation methods for various core-shell nanostructures such as gold-silica and silver-titania nanoparticles. The following Chapters 4 and 5 analyze plasmonic core-shell metal-dielectric nanoparticles embedded in perovskite solar cells. It is shown that using gold@silica or silver@titania NPs results in enhanced photocurrent and thus increased efficiency. After photoluminescence studies, this effect was attributed to an unexpected phenomenon in solar cells in which a lowered exciton binding energy generates a higher fraction of free charge. Embedding thermally unstable silver NPs required a low-temperature fabrication method which would not melt the Ag NPs. This work offers a new general direction for temperature sensitive elements. In Chapters 6 and 7, perovskite film formation is studied. Chapter 6 shows the existence of a previously unknown crystalline precursor state and an improved surface coverage by introducing a ramped annealing procedure. Based on this, Chapter 7 investigates different perovskite annealing protocols. The main finding was that an additional 130°C flash annealing step changed the film crystallinity dramatically and yielded a higher orientation of the perovskite crystals. The according solar cells showed an increased photocurrent attributed to a decrease in charge carrier recombination at the grain boundaries. Chapter 8 presents on-going work showing noteworthy first results for silica scaffolds, and layered, 2D perovskite structures for application in solar cells.
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Cheng, Cheng. "Semiconductor colloidal quantum dots for photovoltaic applications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:07baccd0-2098-4306-8a9a-49160ec6a15a.
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This thesis studies lead suphide (PbS) colloidal quantum dots and their photovoltaic applications. Different sizes of PbS QDs were synthesised and characterised using absorption spectroscopy and transmission electron microscopes. PbS QD Schottky junction devices were fabricated with AM1.5 power conversion efficiency up to 1.8 %. The Schottky junction geometry limits the device performance. A semiconductor heterojunction using ZnO as an electron acceptor was built and the device efficiency increased to 3%. By studying the light absorption and charge extraction profile of the bilayer device, the absorber layer has a charge extraction dead zone which is beyond the reach of the built-in electric field. Therefore, strategies to create a QD bulk heterojunction were considered to address this issue by distributing the junction interface throughout the absorber layer. However, the charge separation mechanism of the QD heterojunction is not clearly understood: whether it operates as an excitonic or a depleted p-n junction, as the junction operating mechanism determines the scale of phase separation in the bulk morphology. This study shows a transitional behaviour of the PbS/ZnO heterojunction from excitonic to depletion by increasing the doping density of ZnO. To utilise the excitonic mechanism, a PbS/ZnO nanocrystal bulk heterojunction was created by blending the two nanocrystals in solution such that a large interface between the two materials could facilitate fast exciton dissociation. However, the devices show poor performance due to a coarse morphology and formation of germinate pairs. To create a bulk heterojunction where a built-in electric field could assist the charge separation, a TiO2 porous structure with the pore size matching with the depletion width was fabricated and successfully in-filled by PbS QDs. The porous device produces 5.7% power conversion efficiency, among one of the highest in literature. The enhancement comes from increased light absorption and suppression of charge recombination.
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Stockhausen, Verena. "Modulation of material properties using Nanoelectrochemistry : from active plasmonic devices and photovoltaic systems to ultrathin electroactive layers." Paris 7, 2011. http://www.theses.fr/2011PA077071.
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L'essor de l'électronique plastique a conduit à une révolution dans la vie quotidienne ces vingt dernières années. Le premier chapitre traite des systèmes hybrides polymères conducteurs/dispositifs plasmoniques. La commutation de l'état électronique du polymère modifie réversiblement les réponses optiques des systèmes plasmoniques. De plus, en jouant sur la nature du polymère, la réponse optique de ces systèmes peut être finement ajustée. Dans le deuxième chapitre, nous aborderons l'étude des films ultraminces électroactifs générés par electroréduction d'un sel de diazonium. Premièrement, le greffage de tels films sans unité centrale benzénique sera développé. Deuxièmement, nous étudierons l'influence du dérivé thiophène attaché à l'unité centrale benzénique, d'une part sur le processus de formation des diazoniums et d'autre part sur les propriétés des films greffés. Le troisième chapitre concerne la fonctionnalisation de surface dite «bottom-up» en surgrefFant des composés monomériques sur les oligomères préalablement déposés. Ceci induit une modification des propriétés du film selon le monomère utilisé et augmente les possibilités de design de films minces électroactifs. Enfin, le quatrième chapitre traitera des cellules photovoltaïques de type Grätzel. Le but étant de fabriquer des cellules photovoltaïques plasmoniques afin d'améliorer les performances du système initial. Les processus de fabrication et la nature de la navette rédox sont d'abord optimisés. Ensuite, plusieurs stratégies pour la déposition de l'or ainsi que les premiers tests d'incorporation seront présentésOver the last twenty years, a continuous increase in plastic electronics has lead to a revolution in lifestyle. In the first chapter, we will discuss hybrid conducting polymer/plasmonic nanoparticle Systems and demonstrate that optical answers of plasmonic structures can not only be reversibly switched according to conducting polymer electronic state. Furthermore, the polymer type induces distinct optical answers, offering tremendous possibilities for further tailoring of optical properties. The second chapter is dedicated to ultrathin electroactive film generation from diazonium salt electroreduction. The first part presents successful diazonium salt derived film deposition without core benzene unit. The second part is devoted to the influence of the thiophene derivative, attached to the core benzene, on diazonium salt generation and electronic properties of gratted films. The third chapter demonstrates that a bottom-up approach can be used to further elongate oligomer chains by overgrafting monomeric compounds. By that, film properties are modified according to the monomer used, enlarging possibilities of distinct electroactive thin film design. In the fourth chapter, we investigate dye sensitized solar cells (DSSC) or Grätzel type cells with regard to the establishment of low cost plasmonic DSSC. By that, we hope to increase efficiencies of the basic System. In a first time, cell setup will be optimized to allow comparison with literature and then, the redox mediator will be replaced in order to optimize the System for subsequent gold incorporation. Finally, several strategies for gold deposition and first tests in cell setup will be demonstrated
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Dooley, Chad Johnathan. "New Nanomaterials for Photovoltaic Applications: A Study on the Chemistry and Photophysics of II-VI Semiconductor Nanostructures." Thesis, Boston College, 2009. http://hdl.handle.net/2345/705.
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Thesis advisor: Torsten FiebigThis dissertation examines the chemistry and photophysics of semiconductor quantum dots with the intent of studying their capabilities and limitations as they pertain to photovoltaic technologies. Specifically, experiments are presented detailing the first time-resolved measurements of electron transfer in electronically coupled quantum rods. Electron transfer from the conduction band of CdTe was measured to occur on the 400 fs timescale (kET = 2.5 x 1012 s-1), more than 500x faster than previously believed. Additionally, the direct optical promotion of an electron from the valence band of CdTe was observed, occurring on the timescale of the pump pulse (~50 fs). Based on the determined injection rates, a carrier separation efficiency of > 90% has been calculated suggesting these materials are sufficient for use in solar energy capture applications where efficient carrier separation is critical. To this end, model photovoltaic cells were fabricated, and their power conversion efficiency and photon-to-current generation efficiency characterized. In devices based of CdSe and heteromaterial quantum rods we observed fill-factors on the order of 10-20% though with power conversion efficiencies of < 0.02%. It was discovered that using a high temperature annealing step, while critical to get electrochemically stable photoelectrodes, was detrimental to quantum confinement effects and likely removed any hQR specific capabilities. Additionally, a detailed study on the role of nucleotide triphosphate chemistry in stabilizing emissive CdS nanoparticles is presented. Specifically it was observed that in a neutral pH environment, GTP selectively stabilizes CdS quantum dots with diameters of ~4 nm while the other naturally occurring ribonucleotides do not yield emissive product. The selectivity is dependent on the presence of the nucleophilic N-7 electrons near a triphosphate pocket for Cd2+ complexation as well as an exocyclic amine to stabilize the resulting product particles. However, in an elevated pH environment, the nucleobase specificity is relaxed and all NTPs yield photo-emissive quantum dots with PLQEs as high as 10%
Thesis (PhD) — Boston College, 2009
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Belchi, Raphaëlle. "Architectures à base de nanostructures de carbone et TiO₂pour le photovoltaïque." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS329/document.
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Le photovoltaïque est une énergie renouvelable pouvant aider à lutter contre le réchauffement climatique et l’épuisement des ressources fossiles utilisées pour la production d’énergie. La filière émergente à base de matériaux pérovskites (photovoltaïque de 3ème génération) est très prometteuse car elle utilise des matériaux abondants et faciles à mettre en œuvre (technologie bas-coût) et a montré de plus des rendements record compétitifs en peu de temps. Il reste cependant des verrous technologiques à lever afin de pouvoir développer cette technologie à grande échelle. L’un deux consiste à améliorer la couche de TiO₂ qui transporte les électrons et dont les défauts limitent les performances et la durée de vie des cellules photovoltaïques pérovskites. Ce travail propose l’utilisation de matériaux à base de nanostructures de carbone et de TiO₂ pour améliorer le transport et la collecte des électrons au sein de ces cellules photovoltaïques et ainsi améliorer leur rendement. Pour cela, la pyrolyse laser, technique singulière de production continue de nanoparticules, a été adaptée pour l’élaboration de nanocomposites TiO₂/graphène aux propriétés contrôlées. Ces matériaux ont été caractérisés puis intégrés aux cellules photovoltaïques pérovskites qui ont démontré une meilleure efficacité en présence de graphène. Par ailleurs, ce travail présente une architecture innovante à base de nanotubes de carbone alignés verticalement, en vue d’une application pour la collecte des électrons photo-générés des cellules photovoltaïques pérovskites. Les matériaux carbonés présentent donc de fortes potentialités pour l’optoélectronique, et plus particulièrement pour le photovoltaïque de 3ème générationPhotovoltaic is a promising renewable energy to tackle global warming and the depletion of fossil resources. The emerging field of perovskite solar cells (3rd generation photovoltaic) is very attractive because it uses abundant and easy-processing materials (low-cost technology) and provides competitive efficiencies.Still, efforts remain to be performed to develop this technology, especially concerning the improvement of efficient and reliable charge transporting electrodes. Titanium dioxide layer, commonly used for electron extraction, presents defects that limit the performance and lifetime of the perovskite solar cells.This work proposes the use of materials based on TiO₂ and carbon nanostructures to improve the electron transport and collection within the solar cells, in order to enhance the power conversion efficiency. The singular technique of laser pyrolysis, which is a continuous process of nanoparticles synthesis, was adapted to produce TiO₂/graphene nanocomposites with well-controlled properties. These materials have been characterized and integrated into perovskite solar cells that demonstrate an improved efficiency in presence of graphene.Besides, this work presents an innovating architecture based on vertically aligned carbon nanotubes for the electron collection of a perovskite solar cell. We show then the strong potential of carbon materials for optoelectronic, especially 3rd generation photovoltaic
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Holder, Jenna Ka Ling. "Quantum structures in photovoltaic devices." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:d23c2660-bdba-4a4f-9d43-9860b9aabdb8.
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A study of three novel solar cells is presented, all of which incorporate a low-dimensional quantum confined component in a bid to enhance device performance. Firstly, intermediate band solar cells (IBSCs) based on InAs quantum dots (QDs) in a GaAs p-i-n structure are studied. The aim is to isolate the InAs QDs from the GaAs conduction band by surrounding them with wider band gap aluminium arsenide. An increase in open circuit voltage (VOC) and decrease in short circuit current (Jsc) is observed, causing no overall change in power conversion efficiency. Dark current - voltage measurements show that the increase in VOC is due to reduced recombination. Electroreflectance and external quantum efficiency measurements attribute the decrease in Jsc primarily to a reduction in InGaAs states between the InAs QD and GaAs which act as an extraction pathway for charges in the control device. A colloidal quantum dot (CQD) bulk heterojunction (BHJ) solar cell composed of a blend of PbS CQDs and ZnO nanoparticles is examined next. The aim of the BHJ is to increase charge separation by increasing the heterojunction interface. Different concentration ratios of each phase are tested and show no change in Jsc, due primarily to poor overall charge transport in the blend. VOC increases for a 30 wt% ZnO blend, and this is attributed largely to a reduction in shunt resistance in the BHJ devices. Finally, graphene is compared to indium tin oxide (ITO) as an alternative transparent electrode in squaraine/ C70 solar cells. Due to graphene’s high transparency, graphene devices have enhanced Jsc, however, its poor sheet resistance increases the series resistance through the device, leading to a poorer fill factor. VOC is raised by using MoO3 as a hole blocking layer. Absorption in the squaraine layer is found to be more conducive to current extraction than in the C70 layer. This is due to better matching of exciton diffusion length and layer thickness in the squaraine and to the minority carrier blocking layer adjacent to the squaraine being more effective than the one adjacent to the C70.
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Kovacik, Peter. "Vacuum deposition of organic molecules for photovoltaic applications." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:98461a90-5ae3-4ae3-9245-0f825adafa72.
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Organic photovoltaics have attracted considerable research and commercial interest due to their lightness, mechanical flexibility and low production costs. There are two main approaches for the fabrication of organic solar cells – solution and vacuum processing. The former relies on morphology control in polymer-fullerene blends resulting from natural phase separation in these systems. The latter takes advantage of solvent-free processing allowing highly complex multi-junction architectures similar to inorganic solar cells. This work aims to combine the benefits of both by depositing conjugated polymers using vacuum thermal evaporation. By employing this unconventional approach it aims to enhance the efficiency of organic photovoltaics through increased complexity of the thin-film architecture while improving the nanoscale morphology control of the individual active layers. The thesis explores the vacuum thermal deposition of polythiophenes, mainly poly(3-hexylthiophene) (P3HT) and side-group free poly(thiophene) (PTh). A variety of chemical techniques, such as NMR, FT-IR, GPC, DSC and TGA, are used to examine the effect of heating on chemical structure of the polymers. Optimal processing parameters are identified and related to the resulting thin-film morphology and charge transport properties. Efficient photovoltaic devices based on polythiophene donors and fullerene acceptors are fabricated. Materials science techniques AFM, XRD, SEM, TEM and MicroXAM are used to characterize topography and morphology of the thin films, and UV-Vis, EQE, I-V and C-V measurements relate these to the optical and electronic properties. The results of the study show that polymer side groups have a strong influence on molecular packing and charge extraction in vacuum-deposited polymer thin films. Unlike P3HT, evaporated PTh forms highly crystalline films. This leads to enhanced charge transport properties with hole mobility two orders of magnitude higher than that in P3HT. The effect of molecular order is demonstrated on polymer/fullerene planar heterojunction solar cells. PTh-based devices have significantly better current and recombination characteristics, resulting in improved overall power conversion efficiency (PCE) by 70% as compared to P3HT. This confirms that the chemical structure of the molecule is a crucial parameter in deposition of large organic semiconductors. It is also the first-ever example of vacuum-deposited polymer photovoltaic cell. Next, vacuum co-deposited PTh:C60 bulk heterojunctions with different donor-acceptor compositions are fabricated, and the effect of post-production thermal annealing on their photovoltaic performance and morphology is studied. Co-deposition of blended mixtures leads to 60% higher photocurrents than in thickness-optimized PTh/C60 planar heterojunction counterparts. Furthermore, by annealing the devices post-situ the PCE is improved by as much as 80%, achieving performance comparable to previously reported polythiophene and oligothiophene equivalents processed in solution and vacuum, respectively. The enhanced photo-response is a result of favourable morphological development of PTh upon annealing. In contrast to standard vacuum-processed molecular blends, annealing-induced phase separation in PTh:C60 does not lead to the formation of coarse morphology but rather to an incremental improvement of the already established interpenetrated nanoscale network. The morphological response of the evaporated PTh within the blend is further verified to positively differ from that of its small-molecule counterpart sexithiophene. This illustrates the morphological advantage of polymer-fullerene combination over all other vacuum-processable material systems. In conclusion, this processing approach outlines the conceptual path towards the most beneficial combination of solution/polymer- and vacuum-based photovoltaics. It opens up a fabrication method with considerable potential to enhance the efficiency of large-scale organic solar cells production.
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Olson, Grant T. "Improving Hybrid Solar Cells: Overcoming Charge Extraction Issues In Bulk Mixtures of Polythiophenes and Zinc Oxide Nanostructures." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1257.
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Organic photovoltaics (OPVs) have received a great deal of focus in recent years as a possible alternative to expensive silicon based solar technology. Current challenges for organic photovoltaics are centered around improving their lifetimes and increasing their power conversion efficiencies. One approach to improving the lifetime of such devices has been the inclusion of inorganic metal oxide layers, but interaction between the metal oxides and common conjugated polymers is not favorable. Here we present two methods by which the interactions between polythiophenes and nanostructured ZnO can be made to be more favorable. Using the first method, direct side on attachment of polythiophene to ZnO nanowires via chemical grafting, we demonstrate chemical linkage between the polymer and ZnO phases. The attachment was confirmed to affect the morphological properties of the polymer layer as well, inducing highly ordered regions of the polymer at the ZnO surface via chemical attachment and physical adsorption. Using the second method to improve polythiophene ZnO interactions, we have functionalized ZnO nanowires with organic molecules that favorably interact with conjugated polymer and organic solvents. Photovoltaic devices were made using a blended active layer of functionalized ZnO nanowires and P3HT. Electrical analysis of the resultant devices concluded that the devices were functional photovoltaic cells and isolated the dominant loss mechanisms for further device improvement.
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Mailhes, Romain. "Effets plasmoniques induits par des nanostructures d’argent sur des couches minces de silicium." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI097/document.
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Le domaine du photovoltaïque en couches minces s’attache à réduire le coût de l’énergie photovoltaïque, en réduisant considérablement la quantité de matières premières utilisées. Dans le cas du silicium cristallin en couches minces, la réduction de l’épaisseur de la cellule s’accompagne d’une baisse drastique de l’absorption, notamment pour les plus fortes longueurs d’onde. Nombreuses sont les techniques aujourd’hui mises en œuvre pour lutter contre cette baisse de performance, dont l’utilisation des effets plasmoniques induits par des nanostructures métalliques qui permettent un piégeage de la lumière accru dans la couche absorbante. Dans ces travaux, nous étudions l’influence de nanostructures d’argent organisées suivant un réseau périodique sur l’absorption d’une couche de silicium. Ces travaux s’articulent autour de deux axes majeurs. L’influence de ces effets plasmoniques sur l’absorption est d’abord mise en évidence à travers différentes simulations numériques réalisées par la méthode FDTD. Nous étudions ainsi les cas de réseaux périodiques finis et infinis de nanostructures d’argent situés sur la face arrière d’une couche mince de silicium. En variant les paramètres du réseau, nous montrons que l’absorption au sein du silicium peut être améliorée dans le proche infrarouge, sur une large plage de longueurs d’onde. Le second volet de la thèse concerne la réalisation des structures modélisées. Pour cela, deux voies de fabrication ont été explorées et développées. Pour chacune d’entre elles, trois briques élémentaires ont été identifiées : (i) définition du futur motif du réseau grâce à un masque, (ii) réalisation de pores dans le silicium et (iii) remplissage des pores par de l’argent pour former le réseau métallique. La première voie de fabrication développée fait appel à un masque d’alumine, réalisé par l’anodisation électrochimique d’une couche d’aluminium, pour définir les dimensions du réseau métallique. Une gravure chimique assistée par un métal est ensuite utilisée pour former les pores, qui seront alors comblés grâce à des dépôts d’argent par voie humide. La seconde voie de fabrication utilise un masque réalisé par lithographie holographique, une gravure des pores par RIE et un remplissage des pores par dépôt d’argent electroless. Les substrats plasmoniques fabriqués sont caractérisés optiquement, au moyen d’une sphère intégrante, par des mesures de transmission, réflexion et absorption. Pour tous les substrats plasmoniques caractérisés, les mesures optiques montrent une baisse de la réflexion et de la transmission et une hausse de l’absorption pour les plus grandes longueurs d’ondeThin-film photovoltaics focus on lowering the cost reduction of photovoltaic energy through the significant reduction of raw materials used. In the case of thin-films crystalline silicon, the reduction of the thickness of the cell is linked to a drastic decrease of the absorption, particularly for the higher wavelengths. This decrease of the absorption can be fought through the use of several different light trapping methods, and the use of plasmonic effects induced by metallic nanostructures is one of them. In this work, we study the influence of a periodic array of silver nanostructures on the absorption of a silicon layer. This work is decomposed into two main axes. First, the influence of the plasmonic effects on the silicon absorption is highlighted through different numerical simulations performed by the FDTD method. Both finite and infinite arrays of silver nanostructures, located at the rear side of a thin silicon layer, are studied. By varying the parameters of the array, we show that the silicon absorption can be improved in the near infrared spectral region, over a wide range of wavelengths. The second part of the thesis is dedicated to the fabrication of such modeled structures. Two different approaches have been explored and developed inside the lab. For each of these two strategies, three major building blocks have been identified: (i) definition of the future array pattern through a mask, (ii) etching of the pattern in the silicon layer and (iii) filling of the pores with silver in order to form the metallic array of nanostructures. In the first fabrication method, an anodic alumina mask, produced by the electrochemical anodization of an aluminium layer, is used in order to define the dimensions of the metallic array. A metal assisted chemical etching is then performed to produce the pores inside the silicon, which will then be filled with silver through a wet chemical process. The second fabrication method developed involves the use of holographic lithography to produce the mask, the pores in silicon are formed by reactive ion etching and they are filled during an electroless silver deposition step. The fabricated plasmonic substrates are optically characterized using an integrating sphere, and transmission, reflection and absorption are measured. All the characterized plasmonic substrates shown a decrease of their reflection and transmission and an absorption enhancement at the largest wavelengths
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Ehrhardt, Fabien. "Elaboration et caractérisation de nanostructures de silicium dans une matrice d'oxynitrure de silicium : applications aux cellules solaires photovoltaïques." Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAD029/document.
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Les phénomènes quantiques des nanostructures peuvent être une opportunité pour le développement d’une nouvelle génération de cellules photovoltaïques. Ce travail décrit la synthèse et les caractérisations de nanoparticules de silicium dans une matrice d’oxynitrure de silicium. Il est possible d’obtenir des nanoparticules de silicium de diamètre compris entre 3 et 7 nm dans des matrices allant du nitrure de silicium à l’oxyde de silicium. Les propriétés des nanoparticules dépendent très fortement de la composition de la matrice. Afin d’accroître la conduction dans ces couches diélectriques, nous avons effectué un dopage électrique par implantation ionique. La localisation et la densité des ions implantés ont été observées par des techniques associées de microscopie électronique en transmission et de rayons X. Une augmentation de la conduction a été démontrée lors du dopage permettant d’observer un effet photovoltaïque sur une structure comportant des nanoparticules de siliciumQuantum effects in nanostructures exhibit properties that can be very useful for the development of a new generation of solar cells. We investigated the synthesis of silicon nanostructures in silicon oxynitride made by a plasma enhanced chemical vapour deposition technique. Thus, silicon nanoparticles of diameter between 3 and 7 nm were obtained in different matrix ranging from silicon oxide to silicon nitride. The properties highly depend on the composition of the matrix. We also study the incorporation of impurities in the films with the aim of increasing the electrical conductivity of the structure. This was done by implanting different ions in the structure followed by thermal annealing. We have investigated the position of the ion and its content in the composite by combining Transmission Electron Microscopy and X-ray diffraction. Finally, N+/P junctions were fabricated using highly doped films containing silicon nanoparticles and a photovoltaic effect was demonstrated
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Xi, Dongjuan. "Nanostructured conjugated polymers for photovoltaic devices." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1619095801&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Löper, Philipp [Verfasser]. "Silicon Nanostructures for Photovoltaics / Philipp Löper." Aachen : Shaker, 2014. http://d-nb.info/1053904584/34.
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Kira, Aiko. "Nanostructured Hybrid Electrodes for Organic Photovoltaic Devices." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/120942.
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Hutter, Oliver S. "Nanostructured copper electrodes for organic photovoltaics." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/71005/.
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This thesis describes a body of original research focused on the development of a viable alternative to the indium-tin oxide (ITO) glass window electrode used in organic photovoltaic (OPV) devices, based on the use of ultra-thin Cu films. The first results chapter describes a low cost, robust Cu | Al bilayer window electrode that simultaneously functions as the low work function electron-extracting electrode and as a sink for oxygen/water molecules in OPVs. When the electrode is exposed to air, an ultra-thin oxide layer forms at its surface without any increase in surface roughness, and the sheet resistance of the electrode actually decreases. However, this electrode has the disadvantage of a lower far-field transparency than ITO glass. The second results chapter describes how the transparency of ultra-thin Cu films can be increased to a level comparable to that of ITO glass across most of the spectrum over which OPVs harvest light using an overlayer of tungsten sub-oxide (WO3-x) which is spontaneously doped with Cu, increasing both its refractive index and electrical conductivity. Unfortunately these electrodes are not air stable. The third results chapter describes how the developments described in the previous two chapters might be integrated to realise an electrode that is both air-stable and highly transparent. The final results chapter describes a very different approach to coupling light into an OPV based on a Cu electrode with a dense array of sub-optical wavelength apertures. These electrodes absorb light strongly, concentrating it as surface plasmon excitations. It is shown that this trapped light can be absorbed by the light harvesting organic semiconductor in organic photovoltaics so that electrodes with very low far-field transparency can perform as well as more transparent electrodes.
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Derkacs, Daniel. "Scattering Properties of nanostructures applications to photovoltaics /." Diss., [La Jolla, Calif.] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3344703.
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Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed March 19, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Miles, David. "Anodized ZnO nanostructures for next-generation photovoltaics." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687389.
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Emerging photovoltaic technologies, such as dye-sensitized solar cells and perovskite solar cells, offer huge potential for providing large-scale and affordable renewable energy to meet our growing power requirements. Central to the success of these technologies is the development of low cost production techniques and materials, often with control of morphological features at the nanoscale. Electrochemical anodization is one example of a technique that can meet these criteria. The aim of this PhD project is to develop ZnO nanostructures using electrochemical anodization and apply them as electron transport materials within dye-sensitized and perovskite solar cells. Aligned arrays of ZnO nanowires were produced by the anodization of zinc foil under mild reaction conditions. A systematic study of the influence of various reaction parameters on the growth of nanowires was conducted and subsequently used to optimise nanowire growth rates. Extremely high growth rates of over 3 μm min-1 were achieved, allowing high aspect ratio nanowires to be produced with lengths in excess of 100 μm. Annealing the nanowire arrays led to the production of polycrystalline ZnO nanowires with an average diameter of 160 nm and a radial slit-type pore structure along their length. Further synthetic modification of these nanowires led to the production of high surface area hierarchical structures. Direct application of the nanowire arrays in back-illuminated dye-sensitized solar cells was found to be unsuccessful due to issues with cracking. However, through the preparation of various pastes using these nanowires, it was possible to produce a range of front-illuminated dye-sensitized solar cell architectures. Whilst the anodic nanowires were found to reduce the efficiency of cells when incorporated within mesoporous ZnO films, they were found to increase the power conversion efficiencies from 1.4 % to 1.9 % when applied as light scattering layers above the mesoporous films. Furthermore, hierarchical core-shell nanostructures, derived from the anodic nanowires, were found to greatly increase the efficiency of quasi-solid state dye-sensitized solar cells with TiO2 photoanodes. Maximum power conversion efficiencies of 7.5 % were achieved through the incorporation of small quantities of these nanostructures. These are amongst the highest reported efficiencies for cells featuring ZnO and quasi-solid state cells in general. The use of ZnO nanostructures, including anodic nanowires, was compared with the use of TiO2 nanoparticles as electron transport materials within perovskite solar cells. Maximum power conversion efficiencies were 50 % lower for cells featuring ZnO rather than TiO2 mesoporous layers. Furthermore, no obvious advantage of using nanowires rather than nanoparticles could be observed. The lower performance of the cells based on ZnO was related to the detrimental thermal degradation of the perovskite material in contact with ZnO. This casts doubt over the use of ZnO nanostructures within perovskite solar cells.
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Boden, Stuart Andrew. "Biomimetic nanostructured surfaces for antireflection in photovoltaics." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/66278/.
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A key consideration in the design of any solar cell is the reduction of reflectance from the top surface. Traditional thin film antireflection schemes are being challenged by new techniques that involve texturing on the subwavelength scale to form ‘moth-eye’ arrays, so called because they are inspired by Nature’s answer to unwanted reflections, the arrays of pillars found on the eyes and wings of some species of moth. In this work, a new method is presented for the optimization of thin film coatings that accounts for the angular and spectral variations in incident solar radiation from sunrise to sunset. This approach is then extended to silicon moth-eye arrays to assess how effectively these surfaces can provide antireflection for silicon solar cells over a full day. The reflectance spectra of moth-eye surfaces are found to depend on the period of the arrays and the height and shape of the pillars, and consequently these parameters can be optimized for the solar spectrum. Simulations predict that replacing an optimized double layer thin film coating with a moth-eye array could increase the full day cell performance by 2% for a laboratory cell and 3% for an encapsulated cell. Compared to a perfectly transmitting interface, this corresponds to losses in short circuit current of only 5.3% and 0.6% for a laboratory and an encapsulated cell, respectively. Furthermore, fabrication of silicon moth-eye arrays by electron beam lithography and dry etching leads to predicted percentage losses at peak irradiance, compared to an ideal antireflective surface, of only 1%. The potentially more scalable technique of nanoimprint lithography is also used to fabricate antireflective moth-eye arrays in silicon, over areas as large as 1 cm2, demonstrating great potential for stealth and antiglare applications in addition to photovoltaics.
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Gérard, Lionel. "Structures de semiconducteurs II-VI à alignements de bande de type II pour le photovoltaïque." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY070.
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Ce travail porte sur l'étude d'hétérostructures de semiconducteurs II-VI à alignements de bande de type II, en particulier sous forme de superréseaux. Il s'agit d'un système qui peut être prometteur pour une application photovoltaïque, et c'est dans cette optique qu'est orienté ce travail. Une première partie traite ainsi d'une réflexion conceptuelle sur l'apport des interfaces de type II au photovoltaïque.Nous présentons ensuite une étude sur la croissance de CdSe et ZnTe par épitaxie par jets moléculaires, sur différents substrats. Ces matériaux sont particulièrement intéressants et adaptés pour cette application car ils ont un gap direct, quasiment le même paramètre de maille, un alignement de bandes de type II, et le CdSe une bande interdite compatible avec le spectre solaire. Mais en contrepartie il s'agit de semiconducteurs binaires qui n'ont aucun atome en commun, de sorte que la croissance d'échantillons avec des épaisseurs précises à la monocouche près constitue un vrai défi. Pour cette raison nous avons procédé à une étude fine des interfaces grâce à des analyses de diffraction de rayons X et de microscopie en transmission, qui nous permet de conclure sur la nature chimique des atomes à proximité des interfaces.Vient ensuite une étude poussée de spectroscopie sur les effets des interfaces de type II sur les porteurs de charges, à travers leur énergie et cinétique de recombinaison. Nous avons développé un modèle analytique qui permet d'ajuster précisément toutes les caractéristiques observées en relation avec ces interfaces, et qui témoigne d'un mécanisme de séparation des charges très efficace. Nous montrons par la suite que ces effets observés sont des caractéristiques intrinsèques de toutes les interfaces de type II, indépendamment des matériaux et des structures, et que ceux-ci nous permettent d'extraire avec précision les valeurs des décalages de bandes entre différents matériaux à alignement de type IIThis work focuses on the study of II-VI semiconductor heterostructures with type II band alignments, especially in the form of superlattices. This is a system that can be promising for photovoltaic applications, and my work is presented in this perspective. Thus the first part deals with a conceptual reflection on the contribution of type II interfaces for photovoltaics.In a second step I present a study on the growth of CdSe and ZnTe by molecular beam epitaxy on various substrates. These materials are particularly interesting and suitable for this application because they have a direct bandgap, are almost lattice-matched, present a type II band alignment, and CdSe shows a bandgap compatible with the solar spectrum. But in return these are binary semiconductors which have no atoms in common, so that the growth of samples with specific thicknesses close to the monolayer is challenging. For this reason we conducted a detailed study at the interfaces through analysis of X-ray diffraction and transmission electron microscopy, which allows us to conclude on the chemical nature of the atoms near the interfaces.This is followed by a detailed spectroscopy study on the effects of type II interfaces on the charge carriers through their energy and kinetics of recombination. We have developed an analytical model that allows to precisely adjust all the features observed in relation to these interfaces, and shows a very efficient charge separation mechanism. We show later that these effects are inherent characteristics of all interfaces of type II, regardless of materials and structures, and that they allow us to accurately extract the values of band offsets between different materials with type II band alignments
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Aslan, Gürel Evren. "Hybrid nanostructured materials : from molecular assemblies to photovoltaic devices /." [S.l.] : [s.n.], 2009. http://opac.nebis.ch/cgi-bin/showAbstract.pl?sys=000274977.
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Goyal, Amita. "Titanium dioxide-germanium nanocomposites for photovoltaic applications." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file Mb., 104 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435250.
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Tam, Wing-yan. "Functional diblock copolymers for nanofabrications and photovoltaic applications." Click to view the E-thesis via HKUTO, 2010. http://sunzi.lib.hku.hk/hkuto/record/B43907301.
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Tam, Wing-yan, and 譚詠欣. "Functional diblock copolymers for nanofabrications and photovoltaic applications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B43907301.
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Auras, Florian. "Solar light harvesting with nanostructured organic and hybrid photovoltaic devices." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-169448.
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Vandamme, Nicolas. "Nanostructured ultrathin GaAs solar cells." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112111/document.
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L’amincissement des cellules solaires semi-conductrices est motivé par la réduction des coûts de production et l’augmentation des rendements de conversion. Mais en deçà de quelques centaines de nanomètres, il requiert de nouvelles stratégies de piégeage optique. Nous proposons d’utiliser des concepts de la nanophotonique et de la plasmonique pour absorber la lumière sur une large bande spectrale dans des couches ultrafines de GaAs. Nous concevons et fabriquons pour ce faire des structures multi-résonantes formées de réseaux de nanostructures métalliques. Dans un premier temps, nous montrons qu’il est possible de confiner la lumière dans une couche de 25 nm de GaAs à l’aide d’une nanogrille bidimensionnelle pouvant servir de contact électrique en face avant. Nous analysons numériquement les modes résonants qui conduisent à une absorption moyenne de 80% de la lumière incidente entre 450 nm et 850 nm. Ces résultats sont validés par la fabrication et la caractérisation de super-absorbeurs ultrafins multi-résonants. Dans un second temps, nous appliquons une approche similaire dans le but d’obtenir des cellules photovoltaïques dix fois plus fines que les cellules GaAs records, avec des absorbeurs de 120 nm et 220 nm seulement. Un miroir arrière nanostructuré en argent, associé à des contacts ohmiques localisés, permet d’améliorer l’absorption tout en garantissant une collecte optimale des porteurs photo-générés. Nos calculs montrent que les densités de courant de court-circuit (Jsc) dans ces structures optimisées peuvent atteindre 22.4 mA/cm2 et 26.0 mA/cm2 pour les absorbeurs d’épaisseurs respectives t=120 nm et t=220 nm. Ces performances sont obtenues grâce à l’excitation d’une grande variété de modes résonants (Fabry-Pérot, modes guidés,…). En parallèle, nous avons développé un procédé de fabrication complet de ces cellules utilisant la nano-impression et le transfert des couches actives. Les mesures montrent des Jsc records de 17.5 mA/cm2 (t=120 nm) et 22.8 mA/cm2 (t=220 nm). Ces résultats ouvrent la voie à l’obtention de rendements supérieurs à 20% avec des cellules solaires simple jonction d’épaisseur inférieure à 200 nmThe thickness reduction of solar cells is motivated by the reduction of production costs and the enhancement of conversion efficiencies. However, for thicknesses below a few hundreds of nanometers, new light trapping strategies are required. We propose to introduce nanophotonics and plasmonics concepts to absorb light on a wide spectral range in ultrathin GaAs layers. We conceive and fabricate multi-resonant structures made of arrays of metal nanostructures. First, we design a super-absorber made of a 25 nm-thick GaAs slab transferred on a back metallic mirror with a top metal nanogrid that can serve as an alternative front electrode. We analyze numerically the resonance mechanisms that result in an average light absorption of 80% over the 450nm-850nm spectral range. The results are validated by the fabrication and characterization of these multi-resonant super-absorbers made of ultrathin GaAs. Second, we use a similar strategy for GaAs solar cells with thicknesses 10 times thinner than record single-junction photovoltaic devices. A silver nanostructured back mirror is used to enhance the absorption efficiency by the excitation of various resonant modes (Fabry-Perot, guided modes,…). It is combined with localized ohmic contacts in order to enhance the absorption efficiency and to optimize the collection of photogenerated carriers. According to numerical calculations, the short-circuit current densities (Jsc) can reach 22.4 mA/cm2 and 26.0 mA/cm2 for absorber thicknesses of t=120 nm and t=220 nm, respectively. We have developed a fabrication process based on nano-imprint lithography and on the transfer of the active layers. Measurements exhibit record short-circuit currents up to 17.5 mA/cm2 (t=120 nm) and 22.8 mA/cm2 (t=220 nm). These results pave the way toward conversion efficiencies above 20% with single junction solar cells made of absorbers thinner than 200 nm
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Carrier, Nathalie. "Indoor photovoltaics with Perovskite solar cells and nanostructured surfaces." Thesis, KTH, Tillämpad fysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-181078.
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Rekemeyer, Paul Harlan. "Nanostructured photovoltaics : improving device efficiency and measuring carrier transport." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108841.
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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 (pages 153-163).
Photovoltaics (PV) offer a promising route to combat climate change. However, the growth rate of the dominant commercial photovoltaic (PV) technology is limited by large capital expenditure requirements. This motivates fundamental research into thin-film materials, such as lead sulfide (PbS) quantum dots (QDs), that are composed of earth-abundant elements, can be produced through low-cost deposition techniques, and are stable under operating conditions. In this thesis, a device architecture that combines a zinc oxide (ZnO) nanowire ordered bulk heterojunction (OBHJ) architecture with band alignment engineering of the PbS QD film to enhance charge extraction is demonstrated. This approach results in PV devices with photocurrent density greater than 30 mA/cm2, which represents a 15% improvement compared to planar devices and enables solar cells with power conversion efficiency up to 9.6%. This photocurrent density is the highest achieved for QDs with a 1.3 eV band gap, which is the optimal band gap in the detailed balance limit. The enhanced photocurrent in the nanowire devices is shown to be a result of both improved light harvesting due to improved in-coupling of light after the addition of the ZnO nanowire array and improved carrier collection due to the bulk heterojunction effect. Furthermore, electron beam-induced current (EBIC) was used to study charge transport in PbS QD films. It is shown that holes are the minority carrier in PbS QD films treated with tetrabutylammonium iodide (TBAI). This finding indicates that the thickness of OBHJ devices composed of a PbS-TBAI film paired with an n-type nanowire array are constrained by minority carrier transport. Moreover, quantitative EBIC was applied for the first time on PbS QD diodes to measure the bulk minority carrier diffusion length (Lbulk). Lbulk was extrapolated by comparing the effective diffusion length measured at different beam energies. EBIC injection leads to high-level injection conditions, therefore a lower bound for the hole diffusion length in PbS-TBAI QD films is established, with Lbulk e 110 nm. This provides a critical design parameter for OBHJ solar cells. This thesis motivates further work on optimization of ZnO nanowire arrays for PbS QD OBHJ solar cells through array patterning, acceptor-doping, and passivation of the nanowire surface. Furthermore, the EBIC technique developed in this work can be applied to quantitatively measure nanoscale carrier diffusion lengths in other thin-film PV materials.
by Paul Harlan Rekemeyer.
Ph. D.
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Liu, Jia. "Fabrication and optical simulation of periodic nanostructures and their applications." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI027/document.
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Les nanostructures périodiques jouent un rôle important dans le domaine des nanotechnologies, en particulier dans le contrôle des photons. Bien qu'il existe de nombreuses techniques d'usage général pour la fabrication et la simulation optique, nous avons développé une technique de fabrication sur mesure et une méthode de simulation optiques pour les structures périodiques pour accélérer le prototypage à l’échelle du laboratoire et la conception optique. Dans la première partie de cette thèse, nous décrivons une technique lithographique nommée « Laser Interference Lithography » (LIL) à faible coût pour la fabrication de nanostructures périodiques. La technique LIL est combinée avec gravure sèche, gravure humide et technique de gravure électrochimique pour réaliser, respectivement, des trous cylindriques, des pyramides inversées et des réseaux taux de pores bi-périodiques à facteur d’aspect élevé sur le substrat à base de silicium. Les modèles unidimensionnels sur des substrats en verre sont également utilisés comme nanofiltres dans la réalisation de la puce de pré-concentration à faible coût. Dans la deuxième partie, nous décrivons d'abord une méthode de calcul électromagnétique rigoureuse Rigorous Coupled-Wave Analysis (RCWA) conçu pour les structures périodiques. Une description détaillée est donnée pour expliquer la méthode numérique. Ensuite, nous combinons la méthode RCWA et une nouvelle approche proposée de la conception des modèles pseudo-désordonnée pour améliorer le piégeage des photons. A titre d'exemple, nous démontrons que, en ajoutant des structures désordonnées à petite échelle sur des arrangements périodiques à grande échelle, la performance quant à l’absorption des couches minces de silicium peut être grandement amélioréePeriodic nanostructures play an important role in the domain of nanotechnology, especially in photon control. While there exist many general purpose techniques for fabrication and optical simulation, we show tailored fabrication and optical simulation methods for periodic structures to accelerate lab-scale prototyping and optical design. In the first part of this dissertation, we describe a low-cost lithographic technique named Laser Interference Lithography (LIL) for fabricating periodic nanostructures. LIL technique is combined with dry-etching, wet-etching and electrochemical etching technique to realize, respectively, cylindrical holes, inverted pyramids and high aspect ratio pore arrays on silicon based substrate. The one-dimensional patterns on glass substrates are also used as nanofilters in realizing low-cost preconcentration chip. In the second part, we first describe Rigorous Coupled-Wave Analysis (RCWA), a rigorous electromagnetic calculation method designed for periodic structures. A detailed derivation is given to explain the numerical method. Then, we combine the RCWA method and a new proposed pseudo-disordered patterns design approach to investigate photon control. As an example, we demonstrate that by adding ‘appropriate’ engineered fine stripes to each long period the absorption performance of thin silicon slab can be largely enhanced
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Botha, Alwyn Francois. "An investigation into the research and development of nanostructured photovoltaic cells." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4301.
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Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Organic semiconductors are used to manufacture thin film (smaller than 50nm) photovoltaic devices. Layer thicknesses are calibrated with the use of an AFM and QCM crystals. An in house method is prepared for solar cell comparison, and AM1.5G (one sun equivalent) testing is performed on manufactured solar cells. The importance of layer thickness and the exciton blocking layers are also highlighted. Numerical modelling of the optical electric field amplitude is done by the transfer matrix method, to take optical interference effects into consideration. The photo generated current was extracted as a function of absorption with varying position in the active layers, and used to excite a general model for organic photovoltaic cells.
AFRIKAANSE OPSOMMING: Organiese halfgeleiers word gebruik vir die vervaardiging van dun-film (kleiner as 50nm) fotovoltaïse toestelle. Laagdiktes is gekalibreer deur die gebruik van ’n AFM en QCM kristalle. ’n Inhuis metode is voorberei vir die vergelyking van vervaardigde selle. Daarna is AM1.5G (een son ekwivalente) toetse uitgevoer op die vervaardigde sonselle. Die belangrikheid van laag dikte en die “exciton” blok lae word ook beklemtoon. Numeriese modellering van die optiese elektriese veld amplitude word gedoen deur die oordrag matriks metode, om optiese interferensie gevolge in ag te neem. Die foto-gegenereerde stroom is as ’n funksie van absorpsie onttrek met wisselende posisie in die aktiewe lae, en is gebruik in ’n algemene model vir organiese fotovoltaïse selle.
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Parker, David. "Structure and photoelectrochemistry of nanostructured II-VI semiconductors for photovoltaic applications." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.681734.
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ZnO nanorods, sensitised to visible light using dyes, quantum dots, or thin films of low-bandgap semiconductors are commonly used as photoanodes in novel solar cells . They have a number of exciting properties for such an application. These include a direct conducting path for electrons, with few grain boundaries, and an increased surface area offering enhanced optical absorption. They are also able to sustain a depletion layer, the electric field this creates can effectively separate charge carriers at the nanorod/sensitiser interface, reducing recombination. However, despite these potential benefits, devices made using 1-D ZnO nanostructures are so far unable to match the performance of devices constructed using mesoporous Ti02 films. One of the reasons given for this is the presence of mid-bandgap states at the surface, which are investigated in this work. ZnO nanorods were grown using a hydrothermal growth technique. Using cyclic voltammetry and photocurrent measurements, mid-band gap trap states were identified and their position found to be centred around 0.8V below the conduction band. Visible luminescence from defect states identified by photoluminescence may be associated with these states. The effects of annealing in air at 180°C, 350°C and 450°C were investigated, all three experimental techniques showed that annealing at temperatures equal to or greater than 350°C was effective in reducing the density of these states. Annealing was also found to have a critical effect on doping density of the nanorods, with implications for both conductivity and the characteristics of the depletion layer that forms at the interface of the nanorods. The doping density was measured using a modified form of MottSchottky analysis and found to be high (> 1020cm-3) for as-grown rods, and only slightly reduced by annealing at temperatures up to 350°C. Annealing at 450°C however reduced the doping density by over two orders of magnitude. These results are consistent with previously reported evidence that incorporated hydrogen acts as a donor for ZnO. A study of the structure of alloyed CdSel-xTex quantum dots was also carried out using a combination of high resolution transmission electron microscopy, selected area electron diffraction and X-ray diffraction. This showed that both wurtzite and zinc blende QDs were present at all compositions, with no clear phase transition between different compositions. CdSe QDs were then successfully used to sensitise annealed nanorods to visible light. Electron transport within the rods was shown to be efficient. The results in this work should prove useful in understanding how best to utilise 1D ZnO nanostructures in solar cells, and provide insights into the nature of defect states which have so far limited the efficiency of such devices.
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Koll, Dominik [Verfasser]. "Three Approaches towards one aim : nanostructured photovoltai devices / Dominik Koll." Mainz : Universitätsbibliothek Mainz, 2015. http://d-nb.info/1075258014/34.
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Zheng, Ying. "Nanostructured thin films for organic photovoltaic cells and organic light-emitting diodes." [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0024921.
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Han, Lu. "Light Management in Photovoltaic Devices and Nanostructure Engineering in Nitride-based Optoelectronic Devices." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1486996393294605.
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Shahroozi, Ali. "Synthesis of novel porous nanostructures via template-directed methods and applications in photovoltaics." Thesis, University of Sussex, 2015. http://sro.sussex.ac.uk/id/eprint/52670/.
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First, PMMA (poly(methyl methacrylate)) colloidal spheres were synthesised using surfactant free emulsion polymerisation (SFEP) process. The effects of temperature, monomer concentration and seeding in the SFEP process were investigated. PMMA colloidal crystals were fabricated using two different self-assembly techniques; the vertical deposition via evaporation and a modified floating (air-water interface) technique. The floating technique made it possible to fabricate 2D and 3D colloidal crystals with controlled thickness through multiple depositions. Once self-assembled, the PMMA colloidal crystals were used as templates to synthesise different 2D and 3D metal oxide inverse opal structures. Different colloidal crystal templating techniques including vacuum assisted and horizontal templating via sol-gel infiltration were used to produce highly ordered inverse opal structures. A comprehensive temperature dependent study on the formation of 3D TiO2 inverse opals was carried out. Successful synthesis of different metal oxide hollow spheres was made possible using a simple sol-gel templating approach. By using seeded polymerisation combined with template-directed synthesis, sphere-in-sphere hollow spheres were successfully synthesised, with independent compositions for both the inner and outer spheres. By using a modified templating technique, it was possible to synthesise bilayered inverse opals with different metal oxide layers. A successful production of such a bilayered/heterojunction system was realised. By using secondary templating combined with a chemical bath deposition (CBD) process, it was also possible to grow ZnO nanorods onto this bilayered inverse opal structure producing a hierarchical hybrid nanostructure. This novel structure was further sensitised by narrow band gap CdSe/ZnS core-shell quantum dots and used in PEC water splitting experiments. The results were very promising and showed stepwise increase in photoefficiency for every step in the synthesis of the novel hierarchical structure of quantum dot sensitised ZnO nanorods on bilayered TiO2/ZnO inverse opal. Increasing surface area, enhancing charge separation, faster charge transport, better light scattering and visible light absorption all played their parts in such a sequential photoenhancing system. Bilayered TiO2/ZnO inverse opal was also used as a photoanode material in dye sensitised solar cell (DSSC) devices and showed improved photoenhancement. The photonic crystal properties of ZnO inverse opal was investigated by coupling it to potassium titanate (K2Ti4O9) nanobelts. Such configuration showed higher photoefficiency in DSSC devices compare to a single system of titanate. In summary, these strategies offer a novel approach for the synthesis of hierarchical structures with each part playing a role in enhancing light harvesting for better energy conversion.
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Cheng, Kai-wing. "Polymers with pendant transition metal complexes for photovoltaic applications and nanofabrications." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B39707544.
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Thierry, François. "Etude des propriétés de nanoparticules semiconductrices pour les cellules solaires hybrides." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4381.
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Cette thèse, réalisée dans l'équipe OPTO-PV du laboratoire IM2NP, porte sur l'étude des propriétés particulières des nanostructures de petites dimensions pour des application optoélectroniques. Pour le solaire photovoltaïque, leur utilisation permet d'augmenter l'efficacité et de réduire les coûts. Après avoir étudié les différentes technologies et phénomènes photovoltaïques, nous avons choisi les cellules hybrides organiques - nanosphères semiconductrices comme structures d'étude. Nous avons alors développé une approche numérique de détermination des propriétés intrinsèques des boîtes quantiques. Notre méthode est rapide et nécessite peu de paramètres pour une utilisation à la fois prédictive et explicative. Nous déterminons les propriétés électronique avec l'approximation de la masse effective en la modifiant pour tenir compte de la non-parabolicité des bandes électroniques. Nous utilisons ces résultats pour évaluer les propriétés optiques, particulièrement l'absorption qui joue un rôle important dans le processus photovoltaïque. Nous prenons en compte des effets de couplages diélectriques sur ces propriétés ainsi que des aspects thermodynamiques. Ces outils nous permettent d'étudier l'effet du confinement quantique des charges sur le comportement optoélectroniques de nanostructures de différents types: multipuits couplés, fils de section circulaire et boîtes sphériques. La réalisation et la caractérisation de couches minces de PMMA incorporant des nanosphères homogènes et (cœur)coquille composées de différents semiconducteurs valident notre approche et posent les bases de l'étude de couches actives hybrides pour la réalisation de cellules solaires performantesThis thesis was conducted in the OPTO-PV team of the IM2NP laboratory. Its aim is to study the peculiar properties of low-dimensional nanostructures for use in optoelectronic applications. For photovoltaics in particular, they can be used for the realization of innovative devices with theoretical hight efficiencies at low costs. After we evaluated the various technologies and phenomena that can be used in nanostructured photovoltaics, we decided to choose an hybrid organic polymer - inorganic quantum dots solar cell as study structure. We then developed a numerical approach to determine the intrinsic properties of quantum dots. Our method is fast and requires few parameters so that we can conduct predictive and explicative studies. We start with the evaluation of the electronic properties under the effective mass approximation that we modify to take into account the non-parabolicity of the energy bands. We use the results to derive the optical properties with emphasis on absorption that plays an important role in the photovoltaic process. We take dielectric coupling effects and also thermodynamic effects into account. Those tools allow the study of the effect of quantum confinement on the optoelectronic behavior of various nanostructures: coupled quantum wells, circular cross-section quantum wires and spherical dots. The fabrication and characterization of PMMA thin-films containing homogeneous and (core)shell quantum dots of different semiconductors, validate our approach and constitute the first step towards the study of hybrid active layers for efficient solar cells
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Cupido, Ian Patrick. "Nitrogen and argon treatment of titanium dioxide nanowire arrays." University of Western Cape, 2021. http://hdl.handle.net/11394/8040.
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>Magister Scientiae - MScTiO2 nanoparticle films are important electron transport layers (ETLs) in photovoltaics such as dye-sensitised, perovskite and polymer hetero-junction solar cells. These films, however, have significant electron trap-sites as a result of the large density of oxygen vacancies present in nano-sized TiO2. These trap-sites cause electron-hole recombination and ultimately lower photon-to-current conversion efficiency of the underlying cell during operation. Doping the TiO2 lattice with low atomic number elements such as nitrogen is a proven method to overcoming the charge transport inefficiency of TiO2 ETLs; another is the use of one-dimensional (1D) nanowires (NWs), instead of nanoparticles.
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Cheng, Kai-wing, and 鄭啟穎. "Polymers with pendant transition metal complexes for photovoltaic applications and nanofabrications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B39707544.
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Hjerrild, Natasha E. "Silver nanowire transparent conductors for quantum dot photovoltaics." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:f1e7821e-1fcc-489b-86d2-13a3298205dd.
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This thesis studies the application of silver nanowire transparent conductors in PbS quantum dot photovoltaics. Silver nanowires were synthesized using a colloidal method and characterized using scanning electron microscopy. Nanowires were deposited on glass substrates by a stamp transfer process to generate a low density continuous network of conductive nanowires. This resulted in a highly conductive and transparent film appropriate for optoelectronic applications. Nanowire synthesis, deposition, and processing were optimised to produce transparent conductors suitable for thin film photovoltaics. These nanowire films were used to fabricate lead sulphide (PbS) colloidal quantum dot solar cells. In this structure, p-type PbS quantum dots form a junction with a n-type ZnO nanoparticle layer. A variety of fabrication and processing treatments were developed in order to reduce short-circuiting of devices and to enhance cell performance. Moderate nanowire density, improved ZnO adherence, slight device aging, and increased PbS film thickness proved to result in the highest quality devices. The champion device developed in this thesis achieved a power conversion efficiency of 2.2%.