Approved for public release; distribution is unlimited / The effects of radiation in GaAs solar cells has been extensively researched and the results of numerous investigation have yielded a considerable amount of information about the degradation in irradiated solar cells. This thesis establishes a novel method in which to use Silvaco's physically-based device simulator, ATLAS, to model the effects of radiation on solar cell output characteristics. A virtual model representing a single junction GaAs solar cell was created in ATLAS. The effects of radiation were modeled using carrier trapping statements representing the defects associated with various fluence levels of 1 MeV electron radiation which were characterized with Deep Level Transient Spectroscopy techniques. The resulting output characteristics of the virtual solar cell, illuminated with a simulated AM0 spectrum, were compared to published experimental measurements for GaAs solar cells of the same dimensions. The virtual solar cell demonstrated a good correlation between the measured and virtual solar cell output characteristics and accurate representation of the spectral response. Complete ATLAS and MATLAB codes are included in appendices. / Major, United States Marine Corps

Approved for public release; distribution is unlimited / The minority carrier diffusion length is a critical parameter in the development of next generation Heterostructure Bipolar Transistors (HBT) and highly efficient solar cells. A novel technique has been developed utilizing direct imaging of electron/hole recombination via an optical microscope and a high sensitivity charge coupled device coupled to a scanning electron microscope to capture spatial information about the transport behavior (diffusion lengths/drift lengths) in luminescent solid state materials. In this work, a numerical model was developed to do a multi-parameter least squares analysis of transport images. Results were applied to the study of transport in materials at the forefront of device technology that are affected by quantum scattering effects, where few reliable experimental measurements exist. The technique allows for easy localization of the measurement site, broad application to a range of materials and potential industrial automation to aid electronics for terahertz devices. / Outstanding Thesis

The purpose of this thesis is to consider PhotoVoltaic Power Converter (PVPC) technology, developed by Atira Technologiesʼ, and its prospects for military and space applications. This research will validate the hypothesis that PVPC technology enables a solar power system to produce usable power during low- and no-light conditions which standard solar power systems fail to provide. Solar cell panels are exposed to sunlight at different angles and with variable intensity, therefore the resulting output power varies depending on the illumination angle as well as the light intensity of each panel. Atira Technologiesʼ devised a novel buck-boost converter that is specifically designed to track the maximum power point of each solar panel. This would provide a significant increase in the overall available power by utilizing a switching topology in a subdued lighting condition. Although a small amount of power is generated, given enough time, a battery will reach its full charge, compared to no additional charging if the battery is using a panel without the circuit. In addition, this research will also show the vital sustaining information to substantiate PVPC's claim of usefulness and effectiveness to allow for longer time on station both in the field and in space so it can extend its missions.

Polymer photovoltaic systems whose photoactive layer is a blend of a semiconducting polymer with a fullerene derivative in a bulk heterojunction configuration are amongst the most successful organic photovoltaic devices nowadays. The three-dimensional organization in these layers (the morphology) plays a crucial role in the performance of the devices. Detailed characterization of this organization at the nanoscale would provide valuable information for improving future material and architectural design and for device optimization. In this thesis, the results of morphology studies of blends of several polyfluorene copolymers (APFOs) blended with a fullerene derivative are presented. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy was combined with dynamic Secondary Ion Mass Spectrometry (dSIMS) for surface and in-depth characterization of the blend films. NEXAFS was performed using two different electron detection methods, partial (PEY) and total (TEY) electron yield, which provide information from different depth regimes. Quantitative compositional information was obtained by fitting the spectra of the blend films with a linear combination of the spectra of films of the pure components. In blends of APFO3 with PCBM in two different blend ratios (1:1 and 1:4 of polymer:fullerene) NEXAFS data show the existence of compositional gradients in the vertical direction for both blend ratios, with clear polymer enrichment of the free surface. A series of APFOs with systematic changes in the side-chains was studied and it was shown that those small modifications can affect polymer:fullerene interaction and induce vertical phase separation. Polymer-enrichment of the free surface was clearly identified, in accordance with surface energy minimization mechanisms, and a compositional gradient was revealed already in the first few nanometers of the surface of the blend films. dSIMS showed that this vertical phase separation propagates throughout the film. It was possible to determine that as the polar character of the polymer increases, and thus the polymer:fullerene miscibility is improved, the tendency for vertical phase separation becomes stronger. / <p>Paper II was not published at the time of the licentiate defence and had the title: NEXAFS spectroscopy study of the surface composition in APFO3:PCBM blend films</p>

M.Sc. / CuInSe2/CdS/ZnO heterojunction solar cells are currently one of the most promising technologies for the production of economically viable energy in the form of electricity. The key component of this thin film solar cell device is the chalcopyrite absorber film. CuInSe2 and its related alloys such as Cu(In,Ga)Se2 have been deposited by a number of techniques, including methods which have been demonstrated to be scalable to mass production volumes. In this study attention was focused on (i) developing a relatively simple deposition technology for the production of chalcopyrite absorber films, (ii) detailed characterization of the semiconductor thin films in terms of the experimental parameters and (iii) fabrication of completed CuInSe2/CdS/ZnO solar cell devices. Metallic precursors comprising of copper and indium were deposited with electron-beam evaporation. The number of elemental layers in the precursor stack as well as the substrate temperature was optimized in order to produce metallic alloys with optimum structural properties. These precursors were subsequently reacted in vacuum to elemental Se vapour or to H2Se/Ar at atmospheric pressure in a separate diffusion reactor. In order to investigate the growth kinetics of the respective processes, the precursors were reacted to the Se in the temperature range between 350°C and 450°C. The structural features (morphology, presence of crystalline phases and bulk compositional properties) of the respective films were compared and correlated against the growth parameters. From this systematic study, optimum growth parameters were determined for the production of completed solar cell devices. / Professor V. Alberts

本論文示範了兩款過渡金屬硫化物量子點 (二硫化銀銦量子點與硫化錳量子點) 在量子點敏化太陽能電池上作為光敏化劑的應用，這也是它們在量子點敏化太陽能電池上的初次應用。 / 二硫化銀銦量子點的合成採用了一鍋合成法，合成的量子點隨後透過3-巰基丙酸連接到二氧化鈦的表面。研究發現，當量子點溶液的濃度處於較低水平的時候，量子點在二氧化鈦的吸附量會較高。另外，從不同研究小組在量子點吸附行為的報告中，觀察到量子點的吸附行為決定於實驗條件，如量子點的大小和表面活劑，納米二氧化鈦多孔膜的孔隙度和量子點的溶劑。實驗中，最高性能的二硫化銀銦量子點敏化太陽能電池的短路電流為0.49 mA/cm²，開路電壓為0.245 V，填充因子為38.26 %，光電轉換效率為0.046 %。 / 透過連續離子層沉積反應法，硫化錳量子點生長並組裝到二氧化鈦的表面上。能譜測量顯示，錳跟硫的比率在不是1:1。這現象懷疑是源於錳(2+)的小離子半徑，對錳(2+)和硫(2-)之間的化學反應產生了不良的影響，導致吸附了的錳(2+)沒有反應過來。通過優化連續離子層沉積反應法週期的數量，最高性能的硫化錳量子點敏化太陽能電池的短路電流為0.65 mA/cm²，開路電壓為0.30 V，填充因子為48.21 %，光電轉換效率為0.095 %。 / QD-SSCs sensitized with novel transition metal sulfides have been demonstrated. Both AgInS₂ QD-SSC and MnS QD-SSC presented in this thesis are new and are the first demonstrated works in the research field. / AgInS₂ QDs was synthesized by one-pot hot colloidal synthesis approach. The as-synthesized QDs were attached to the TiO₂ surface through 3-mercaptopropionic acid. Optimization process on QDs adsorption was done, and it has been observed that the amount of QDs adsorbed is higher when the concentration of the QDs solution is at low level. The variations in the behaviors in QDs adsorption between works from different research groups are considered to originate from experimental conditions such as the sizes and surfactants of QDs, porosities in the TiO₂ matrix, and the solvent for QDs dispersion. The optimized AgInS₂ QD-SSC attained a short-circuit current of 0.49 mA/cm², an open-circuit voltage of 0.245 V, a fill factor of 38.26 % and a power conversion efficiency of 0.046 %. IPCE measurements confirm the successful sensitization from AgInS₂ QDs, indicating the energetically favourable electron injection from AgInS₂ QDs to TiO₂. / By adopting the SILAR technique, MnS QDs was in-situ grown and deposited on the TiO₂ surface. EDX measurements indicated that the Mn/S ratio in the TiO₂/MnS film is not 1:1. The reason is suspected to originate from the small ionic radius of Mn²⁺ that promoted an adverse effect on the reaction between Mn²⁺ and S²₋. It is proposed that a portion of the adsorbed Mn²⁺ did not react with the S²₋., resulting an excess concentration of Mn²⁺ in the film. By optimizing the number of SILAR cycles, MnS QD-SSC was optimized to exhibit a short-circuit current of 0.65 mA/cm², an open-circuit volatge of 0.30 V, a fill factor of 48.21 % and a power conversion efficiency of 0.095 %. IPCE measurements confirm the sensitization is originated from MnS QDs, which consequently reveal an energetically favourable electron injection from the MnS QDs to TiO₂. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Cheng, Kai Chun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Solar cells --- p.2 / Chapter 1.2.1 --- Developments --- p.2 / Chapter 1.2.2 --- Nanostructured solar cells --- p.4 / Chapter 1.2.2.1 --- Bilayer organic solar cells --- p.4 / Chapter 1.2.2.2 --- Bulk heterojunction organic solar cells --- p.5 / Chapter 1.2.2.3 --- Organic-inorganic hybrid solar cells --- p.7 / Chapter 1.2.2.4 --- Dye-sensitized solar cells --- p.8 / Chapter 1.2.2.5 --- Quantum dot-sensitized solar cells --- p.11 / Chapter 1.2.3 --- Characterization of solar cells --- p.11 / References --- p.14 / Chapter Chapter 2 --- Quantum dot-sensitized solar cells --- p.18 / Chapter 2.1 --- Quantum dots --- p.18 / Chapter 2.1.1 --- Quantum confinement --- p.18 / Chapter 2.1.2 --- Multiple exciton generation --- p.20 / Chapter 2.2 --- Quantum dot-sensitized solar cell --- p.22 / Chapter 2.2.1 --- Principles --- p.22 / Chapter 2.2.2 --- Assembly of oxide/quantum dot film --- p.25 / Chapter 2.2.3 --- Light harvesting and electron injection --- p.29 / Chapter 2.2.4 --- Titanium dioxide as electron acceptor --- p.33 / Chapter 2.2.5 --- Redox process of electrolyte --- p.37 / Chapter 2.2.6 --- Counter electrode materials --- p.39 / References --- p.41 / Chapter Chapter 3 --- Experimental Details --- p.45 / Chapter 3.1 --- Materials --- p.45 / Chapter 3.2 --- Preparation of the TiO₂ mesoporous film --- p.46 / Chapter 3.3 --- Synthesis of AgInS₂ quantum dots --- p.47 / Chapter 3.4 --- Preparation of the TiO₂/QDs film --- p.47 / Chapter 3.5 --- Configuration of the QD-sensitized solar cell --- p.49 / Chapter 3.6 --- Characterization and Photoelectrochemical Measurements --- p.51 / References --- p.52 / Chapter Chapter 4 --- Experimental Results --- p.53 / Chapter 4.1 --- AgInS₂ QD-sensitized solar cell --- p.54 / Chapter 4.1.1 --- Characterization of AgInS₂ QDs --- p.54 / Chapter 4.1.2 --- Adsorption of AgInS₂ QDs on the TiO₂ surface --- p.56 / Chapter 4.1.3 --- Photoelectrochemical measurements of the AgInS₂ QD-SSC --- p.60 / Chapter 4.2 --- MnS QD-sensitized solar cell --- p.64 / Chapter 4.2.1 --- Characterization of MnS QDs --- p.64 / Chapter 4.2.2 --- Photoelectrochemical measurements of the MnS QD-SSC --- p.69 / References --- p.74 / Chapter Chapter 5 --- Discussions and Conclusions --- p.75 / Chapter 5.1 --- Discussions --- p.76 / Chapter 5.1.1 --- AgInS₂ QD-SSC --- p.76 / Chapter 5.1.1.1 --- Adsorption of AgInS₂ QDs on the TiO₂ surface --- p.76 / Chapter 5.1.1.2 --- Electron injection --- p.80 / Chapter 5.1.1.3 --- Problems encountered and future directions --- p.83 / Chapter 5.1.2 --- MnS QD-SSC --- p.84 / Chapter 5.1.2.1 --- Growth of MnS QDs on the TiO₂ surface --- p.85 / Chapter 5.1.2.2 --- Effects of SILAR cycles on MnS QD-SSC --- p.86 / Chapter 5.1.2.3 --- Problems encountered and future directions --- p.88 / Chapter 5.1.3 --- AgInS₂ QD-SSC versus MnS QD-SSC --- p.89 / Chapter 5.2 --- Conclusions --- p.91 / References --- p.94

Ma, Xuhang = 柔性襯底銅銦鎵硒太陽能電池製備工藝 / 馬續航. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 88-91). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Ma, Xuhang = Rou xing chen di tong yin jia xi tai yang neng dian chi zhi bei gong yi / Ma Xuhang.

The development of mesoporous titania (meso-TiO2) films is a considerable research goal in the field of mesoporous material development due to their proven applicability in solar cells and phtocatalysts. In this work, the meso-TiO2 films were fabricated through different methods and these home-made titania structures were applied in DSSCs and photocatalysts. Meso-TiO2 powders were first prepared from ethanol/water or ethanol solvent. The meso-TiO2 made from the ethanol/water solvent did not have an ordered mesostructure, but that made from ethanol solvent had 2D-hexagonal mesostructure. Films were prepared by adding ordered meso-TiO2 particles into paste formulations of P25 nanoparticles with weight proportion ranging from 0 to 100%. These were used to form films by doctor blading, and the influence of paste composition on film structure, morphology, porosity, optical properties and cell performance were investigated. Secondly, ordered meso-TiO2 films were fabricated by dip coating from aqueous or ethanol solvent. Both films had cubic mesostructures, but the film coated from aqueous solvent was not uniform. The film formed from ethanol solvent was doped with sulphur. The effects of doping on the mesostructure, morphology, structure, optical properties and photocatalytic activity were studied. The thickness of films was increased by repeated coating. The number of layers had an influence on the mesostructure, morphology, optical properties and cell performance when these films were applied in DSSCs Finally, a novel method was adopted to prepared meso-TiO2 films. Molecular titania precursors or titania colloidal seeds were used as the titania source. Both of them can be used to prepare free-standing hybrid films at air-water interface by a self-assembly method, however the one synthesised from the molecular titania precursor did not contain very much titania and became a powder after calcination. In contrast, after calcination, the films formed from the colloidal titania solution remained intact, and were composed of mixtures of TiO2 nanoparticles and nanowires with mesopores arising from interparticle porosity. These films were applied in DSSCs. This interfacial method was also successfully extended to prepare free-standing ZnO films from a molecular precursor. After calcination, the free-standing ZnO films were found to be composed of rough spheres formed by flocculation of smaller nanoparticles.

Perovskite photovoltaics is one of the fastest growing opto-electronic technologies with device efficiencies currently exceeding 23%. The opportunity to deposit these abundant materials with large area solution processing techniques could make perovskites viable for low-cost production. However, since perovskite materials are prone to degradation, their lifetime needs to be improved to that of silicon solar cells before these devices can be commercialized. Moreover, unlike most semiconductors, trap densities in polycrystalline perovskite films in high-performing devices have been determined to be relatively large, suggesting a remarkable defect tolerance in perovskite films that needs to be understood in the context of the nature of the trap states and any residual non- radiative losses. These non-radiative losses are observed as photoluminescence heterogeneity within perovskite films, even for high-performing perovskite systems. In this work, we explore the degradation kinetics of perovskite devices under stress conditions and find that further stability improvements should focus on the mitigation of trap generation during ageing. Furthermore, we fabricate perovskite solar cells with a novel back-contact structure, in which electron- and hole-selective electrodes are co-positioned on the back side of the cell and spaced by 100 μm. By utilising grazing-incidence X-ray diffraction, we show that even in the earliest stages of conversion of precursors to perovskite we achieve remarkably high open-circuit voltages, suggesting that the defect tolerance of perovskites appears at an early stage in the conversion process. Moreover, we employ scanning X-ray diffraction with nanofocused beam and obtain detailed information, revealing overlapping grains located at different depths within perovskite films. We find that the critical grain size is the longer-range structural super-grains rather than the grains viewed with conventional microscopy techniques. These findings further highlight the presence of structural defects in perovskite materials and provide important insights towards improving the optoelectronic behaviour of these materials.

Orientador: Francisco Carlos Lavarda / Banca: Luiz Carlos da Silva Filho / Banca: Fernando Sato / O Programa de Pós Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atvidades de pesquisa de diversos campi / Resumo: Atualmente existe uma intensa busca por novos materiais com propriedades ajustadas para utilização em células solares orgânicas de modo de obter um aumento em sua eficiência de conversão para que possa substituir os dispositivos de silício. O politieno [3,4-b]-tiofeno-co-benzoditiofeno (PTB7) é um polímero recentemente proposto na literatura e com propriedades muito interessantes em células solares orgânicas, o que o coloca como uma possível alternativa ao amplamente utilizado poli(3-hexiltiofeno) (P3HT). Tem sido relatadas modificações diferentes posições da unidade monomérica deste copolímero, tanto na etrutura benzoditiofeno (BDT), quanto no estrutura tienotiofeno (TT), que o compõe. Estas modificações levaram a novos polímeros com propriedades diferentes e por vezes mais interessantes que aquelas do PTB7 sem substituições. O trabalho que será apresentado visou estudar as propriedades estruturais, eletrônicas e ópticas do PTB7 e possíveis alterações ocorridas devida às modificações químicas realizadas na estrutura do BDT de suas unidades monoméricas. Tal estudo utilizou ferramentas de otimização de estruturas como Mecânica Molecular, Dinâmica Molecular e o método semi-empírico Parametric Method 6 (PM6), assim como de cálculo de estrutura eletrônica de materiais, como a Teoria do Funcional da densidade (DFT) e de cálculos de propriedades ópticas como a Teoria do Funcional da Densidade Dependente do Tempo (TD-DFT). Concluímos que o PTB7 no estado sólido pode ser considerado planar. Com o nosso modelo para o PTB7, obtivemos uma diferença de energia entre o Último Orbital Molecular Ocupado HOMO (do inglês Highest Occupied Molecular Orbital) e o Primeiro Orbital Molecular Desocupado LUMO (do inglês Lowest Unoccupied Molecular Orbital) de aproximadamente 1,84 eV, sendo que este valor está em boa concordância com o valor experimental. Em relação às substituições químicas, estudamos... / Abstract: Currently there is an intensive search for new materials with turned properties for use in organic solar cells to obtain an increase in its conversion efficiency and replace silicon devices. The polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) is a polymer recently proposed in the literature and with very interesting properties in organic solar cells, which places it a a possible alternative to the widely used poli(3-hexilthiophene) (P3HT). It has been reported changes in different positions of the monomeric unit of this copolymer, both in benzodithiphene (BDT) structure, as in the thienothiphene (TT) structure that compose it. These modifications led to new polymer with different properties and sometimes more interesting than those of PTB7 without substituions. The work to be presented aimed to study the structural, electronic and optical properties of PTB7 and possible changes due to chemical changes made in the BDT structure of its monomeric units. This study employed optimization tools like Molecular Mechanics, Molecular Dynamics and Parametric Method 6 (PM6), as well as calculations of the electronic structures with the Density Functional Theory (DFT) method, and optical properties such as the Time Dependent Density Functional Theory (TD-DFT) calculations. We conclude that the PTB7 chains in the solid state can be considered planar. With our model for PTB7, we obtained a difference between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) of approximately 1.84 eV, and this value is in good agreement with the experimental value. Regarding chemical substantions, we studied theoretically 8 derivatives of PTB7 and the results showed that it is possible to obtain compounds with a significant decrease in and that it is possible to obtain compounds with HOMO and LUMO energy values more adjusted to the widely employed acceptor material phenyl-C61-butyric acid methyl ester (PCBM) / Mestre