A geração de energia fotovoltaica continua em crescimento e por isso estudos relacionados à aplicação de diferentes tecnologias fotovoltaicas se tornam muito importantes. A tecnologia de células fotovoltaicas de silício cristalino representa a maior parte da aplicação de energia solar fotovoltaica atualmente. Os módulos com tecnologias de filmes finos foram apresentados ao mercado como uma nova geração de módulos e atualmente são referenciados como módulos fotovoltaicos de segunda geração. As tecnologias de filmes finos possuem algumas vantagens em relação ao silício cristalino, como por exemplo: menor quantidade de material, menor custo de produção e possibilidade de se produzir células e módulos flexíveis, embora em geral apresentem eficiências menores. Existem tecnologias de filmes finos aplicadas à geração fotovoltaica que apresentam instabilidade quando expostas à radiação solar, variando a potência gerada do módulo nas primeiras horas de exposição. Esses efeitos motivaram a padronização de um ensaio de exposição solar, do inglês light-soaking, que atualmente é previsto por uma norma internacional de qualificação de módulos fotovoltaicos (IEC 61646). Neste trabalho, desenvolveu-se uma metodologia para realizar o ensaio lightsoaking e construiu-se uma bancada de testes para obter resultados experimentais a partir de módulos expostos na cobertura do prédio anexo do LABSOL. Para isso, foi realizada uma análise de área livre de sombra disponível, bem como montada a estrutura metálica de sustentação para os módulos. Também foram instaladas resistências elétricas para dissipação de potência dos módulos e montado painel elétrico dentro do prédio centralizando as conexões necessárias. O experimento também contou com o desenvolvimento de um programa em linguagem Visual Basic® para interagir com os instrumentos de medição e realizar o monitoramento do ensaio. Neste trabalho foram ensaiados quatro módulos com diferentes tecnologias de filmes finos, as quais: silício amorfo com tripla junção, silício amorfo com uma junção, CIGS (Disseleneto de Cobre, Índio e Gálio) e por último dupla junção de silício amorfo com silício microcristalino. O experimento foi conduzido por 55 dias, sendo que a cada minuto o programa registrou dados de irradiância, irradiação acumulada e temperatura dos módulos. Ao final do experimento, os módulos receberam no total 347 kWh/m2 de irradiação e, durante o ensaio, foram realizadas ao todo 8 medições de curva característica corrente versus tensão para verificar o desempenho dos módulos. Antes e após a exposição, também foram realizadas medições em um simulador solar a fim de se obter medidas em condições controladas de temperatura e irradiância. Ao aplicar o critério de estabilização previsto na norma IEC 61646, verificou-se que todos os módulos o atenderam. Contudo, os módulos com tecnologia de uma junção de silício amorfo e com tecnologia de tripla junção de silício amorfo voltaram a apresentar degradação acima do máximo estabelecido pela norma IEC 61646 após continuarem expostos à radiação solar. Sendo assim, pode ser necessário alterar o critério para um maior valor de irradiação acumulada entre cada avaliação de degradação destes módulos, principalmente quando o ensaio é realizado com temperatura externa elevada. A metodologia mostrou que esse ensaio pode ser realizado em ambiente externo com luz natural de maneira prática e econômica, porém realizar as medições de curva característica com luz natural e temperatura não controlada implica em adicionar algumas incertezas ao ensaio. / The photovoltaic (PV) power generation continues to grow and so studies related to the application of different photovoltaic technologies become very important. The crystalline silicon solar cells technology is the most current application of PV power generation. The photovoltaic modules with thin film technologies were presented to the market as a new generation of modules and are currently referred to as second generation PV modules. The thin film technologies have some advantages compared to crystalline silicon, for example, less material, lower cost of production and ability to produce flexible cells and modules, although generally have lower efficiencies. There are thin film technologies for photovoltaic conversion that show instability when exposed to the sun, varying the power generated in the early hours of sun exposure. These effects led to the standardization of a sun exposure test, the light-soaking test, which is currently standardized by an international standard of qualification of photovoltaic modules (IEC 61646). In this study, we developed a methodology to perform the light-soaking test and built a workbench to obtain experimental results from PV modules set out in the LABSOL building. For this purpose, a shadow analysis was performed as well as the metal structure mounted to support the photovoltaic modules. Resistive loads were also installed in order to dissipate the power of the modules. An electrical panel was mounted inside the building to centralize the necessary connections. The workbench also included the development of a program in Visual Basic® to interact with the measuring instruments and carry out the monitoring of the experiment. In this work we tested four modules with different thin film technologies, including: triple junction amorphous silicon, single junction amorphous silicon, CIGS (Copper Indium Gallium Diselenide) and tandem junction of amorphous silicon and microcrystalline silicon. The experiment was conducted over 55 days, and every minute the program recorded irradiance data, accumulated irradiation and module temperature. At the end of the experiment, the modules received 347 kWh/m2 of irradiation. During the test, there were a total of 8 characteristic curve (I x V) measurements to verify the performance of the modules. Before and after exposure, were also performed measurements in a solar simulator. By applying the stabilization criteria presented in IEC 61646 it was found that all the modules have been considered stabilized. However, after being exposed to more hours of sunlight, the single junction amorphous silicon module and the triple junction amorphous silicon module presented degradation above the maximum established by IEC 61646 standard. Thus, it may be necessary to change the criteria for a higher value of accumulated irradiation between assessments of degradation of these modules, especially when the test is performed with high external temperature. The methodology showed that this test may be performed outdoors under natural light in a practical and economical way, but the characteristic curve measurements with natural light and uncontrolled temperature add some uncertainty to the test.

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-01-21T10:10:35Z No. of bitstreams: 0 / Made available in DSpace on 2015-01-21T10:10:35Z (GMT). No. of bitstreams: 0 / Tendo em vista a Economia do Hidrogênio e sua infinidade de possibilidades, este trabalho estuda a geração de hidrogênio utilizando a energia solar fotovoltaica. Tendo em vista o consumo mundial de energia crescente, novos métodos de produção energética tem que ser levados em consideração, como o fato do hidrogênio ser um vetor energético de baixo impacto ambiental. Por outro lado, as reservas de combustíveis fósseis não serão capazes de satisfazer essa demanda em longo prazo e seu uso contínuo produz efeitos colaterais, como a poluição que ameaça a saúde humana e os gases de efeito estufa associados à mudança climática. No contexto do Brasil, a eletrólise da água combinada com as energias renováveis e células a combustível seriam uma boa base para melhorar o fornecimento de energia distribuída. Propõe-se, no presente trabalho, produzir hidrogênio por energia renovável, especificamente pelo acoplamento direto de um gerador fotovoltaico a um eletrolisador alcalino de água experimental, concebido localmente. Busca-se entender as características inerentes da interação desses dispositivos, encontrar as eficiências de cada etapa do sistema montado, assim como a eficiência global, adquirindo uma noção mais precisa e prática do uso da energia solar fotovoltaica na alimentação de um eletrolisador. Os resultados experimentais evidenciaram que a transferência da energia do gerador fotovoltaico ao eletrolisador depende fortemente das condições instantâneas climáticas e do modo como estes estão conectados. A interdependência entre variáveis foi reproduzida pelas investigações com destaque para: densidade de corrente no eletrolisador, potencial elétrico, irradiância solar, concentração do eletrólito, área do eletrodo e dimensões da célula eletrolítica. A eficiência do eletrolisador alcançada foi de 21%. A eficiência global (irradiância solar - hidrogênio) foi de 2%. O presente estudo dá subsídios para que seja dimensionado o acoplamento do sistema eletrolisador - gerador FV a partir de uma célula eletrolítica buscando-se minimizar perdas. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Orientador: Ennio Peres da Silva / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-20T13:25:32Z (GMT). No. of bitstreams: 1 Strangueto_KarinaMaretti_M.pdf: 19906367 bytes, checksum: cfc584b8248827cae84c86e393a1870f (MD5) Previous issue date: 2012 / Resumo: Desde a Revolução Industrial, as atividades desenvolvidas pelo homem têm provocado um crescimento maciço das emissões de gases de efeito estufa e poluentes para a atmosfera da Terra, devido, entre outros fatores, à constante e crescente necessidade de energia. Um grande esforço vem sendo realizado nas últimas décadas para a redução dessas emissões, com especial atenção ao setor de transporte, principalmente pelos efeitos provocados nas populações das grandes cidades devido à concentração de veículos em espaços reduzidos. Neste caso, busca-se aumentar: a eficiência dos veículos convencionais, o uso de biocombustíveis e de veículos híbridos, e, mais recentemente, o uso de veículos elétricos (VEs). Com o avanço da utilização de veículos elétricos como meio de transporte "limpo", são necessários maiores estudos para avaliar a quantidade de energia necessária para o abastecimento das frotas destes veículos e, também, uma análise da quantidade evitada de emissões de gases de efeito estufa (gás carbônico) comparativamente aos modelos à combustão interna. Assim, esse trabalho teve como objetivo desenvolver esses temas. A geração de energia através painéis fotovoltaicos foi a escolha para essa dissertação, onde foi realizado um estudo de caso para uma usina de 1 MWP, determinando a quantidade de energia efetivamente produzida, considerando a usina localizada em Campinas, São Paulo. Dessa forma, pôde-se estimar que a frota de veículos que poderia ser abastecida com a energia gerada por essa usina teria um valor entre 955 e 1.118 veículos, dependendo de diferentes logísticas de abastecimento consideradas. Com a frota estimada, também foi possível calcular que emissões de até 2.004 toneladas anuais de CO2 poderiam ser evitadas pela substituição dos veículos convencionais pelos por esta frota de VEs / Abstract: Since the Industrial Revolution, human activities have been causing a massive growth in greenhouse gases and pollutants emissions to the Earth's atmosphere, due to, between other factors, the continuing and growing need for energy. A great effort has been made in recent decades to reduce these emissions, with special attention to the transport sector, mainly caused by the effects on populations of large cities due to the concentration of vehicles in confined spaces. In this case, seeks to improve: the efficiency of conventional vehicles, the use of biofuels and hybrid vehicles, and, more recently, the use of electric vehicles (EVs). With advancing of Electric Vehicle use as a means of "green" transport, more studies are needed to assess the amount of energy required to supply fleets of this kind of vehicles and, also, an analysis of the amount of avoided emissions of greenhouse gases (carbon dioxide) compared with internal combustion models. Thus, this study aimed to develop these themes. The generation of energy through photovoltaic panels was the choice for this dissertation, which was conducted a case study for a generating station of 1 MWP, determining the amount of energy effectively produced, considering the generating station located in Campinas, Sao Paulo. Thus, it was estimated that the fleet of vehicles that could be supplied with energy generated by this plant would have a value between 955 and 1.118 vehicles, depending on different logistical supply considered. With the fleet estimated, it was also possible to calculate that 2.004 tons of CO2 could be avoided by the replacement of conventional vehicles by EVs / Mestrado / Engenharia Mecanica / Mestre em Planejamento de Sistemas Energéticos

Le procédé Kyropoulos est un procédé de croissance cristalline par trempe de germe permettant potentiellement de produire des lingots de silicium de haute qualité pour des applications photovoltaïques. Un modèle numérique 3D du processus, avec modélisation de la thermique, de la mécanique des fluides et de la solidification, a été créé pour développer un prototype expérimental de croissance Kyropoulos pour le silicium. Le dispositif a un creuset de forme carrée chauffé par trois sources thermiques (haut, bas, coté). La simulation numérique a permis de comprendre l’effet couplé, entre rayonnement et mécanique des fluides dans le bain, sur la solidification. L’étude Numérique a montré que la forme du cristal est dépendante de l’écoulement dans le bain et le rayonnement. Le procédé est sensible à la croissance asymétrique sous l’effet conjugué entre la mécanique des fluides et le changement d’émissivité du silicium durant la solidification. L’application des bons paramètres de chauffage et l’homogénéisation du bain ont permis de contrôler la croissance latérale du cristal. Par conséquence, des cristaux symétriques ont été obtenus numériquement et expérimentalement. L’étude numérique a montré la possibilité de contrôler la forme de la section horizontale du cristal, par diffusion thermique et par convection, pour obtention d’un lingot à section horizontale carrée sans contact avec le creuset.Le prototype expérimental développé a permis de faire croitre des cristaux de silicium monocristallin. Le procédé a stabilisé la croissance facettée donants des cristaux avec une section horizontale carrée grâce à la cinétique de croissance des facettes <111> dans le silicium donnants des mono cristaux de section horizontale de forme carré. / Kyropoulos technique is a top seeding process with the potential to produce high quality silicon ingots for photovoltaic applications. The crystal grows inside the melt in an unconfined low stress growth environment. A 3D numerical model of the full process, including heat transfer fluid dynamics and solidification, was created to develop a working experimental prototype of the process for silicon. The process had a square crucible heated by three heaters (top, bottom, side).Numerical simulation explained the complex coupled effect of radiation and melt flow on the solidification process. The study showed that the shape of the crystal is dependent on the melt flow. The growth was found to be sensitive to symmetry loss due to a strong coupled effect between melt flow and emissivity change of silicon during solidification. Control of heating parameters and homogenization of the melt flow allowed a consistent symmetric crystal growth. As a consequence, symmetric silicon crystals were obtained experimentally and numerically. Numerical investigation showed the possibility to control thermally, by heat diffusion and convection, the shape of the horizontal cross section to obtain a square ingot.The developed experimental prototype succeeded to grow monocrystalline silicon crystals. The process stabilized faceted growth in the <111> direction. The faceted monocrystalline crystals had a square horizontal cross section.

Cette recherche se concentre sur l'optimisation d'un micro-réseau en interaction avec le réseau électrique intelligent. Il s'agit de la recherche de solutions optimales pour la conception d'un micro-réseau afin de minimiser les coûts, d'une part, et la possibilité augmenter 1'utilisation des sources renouvelables, d'autre part. La supervision, doit traiter la prise en compte des incertitudes dans la gestion prédictive optimisée des flux de puissance. / This thesis study focuses on a DC microgrid building-integrated satisfying the power balance at the local level and supplying DC loads during both, grid-connected and isolated operation modes. Considering that energy management can be defined as a group of different control strategies and operational practices that together with the new physical equipment and software solutions aims to accomplish the objectives of energy management, the main objective of this thesis is to define the energy management strategies for the building-integrated DC microgrid, aiming to keep the bus voltage stable as well as to reduce the energy cost to the end users and the negative impact to the main grid. Therefore, this research work focuses to optimize and develop the implementation of the designed controller of building-integrated DC microgrid. The proposed DC microgrid consists of PV building-integrated sources, a storage system, a main grid connection for the grid-connected mode and a micro turbine for the off-grid or isolated mode, and a DC load (electric appliances of a tertiary building). The bidirectional connections with the main grid and the storage aim to supply the building’s DC appliances, and sell or store the energy surplus. The results validate the operation of the whole system, ensuring the capability of the proposed supervisory control to manage the energy power flow while ensuring voltage stability. Other goals concern the analyze of the proposed separation between optimization and real time power balance and the usage of the proposed load shedding/restoration algorithm in the microgrid environment are also validate. Regarding the technical contributions, the work of this thesis allowed the creation and the practical development of a test bench for microgrid based on PV sources emulator, which allows the repeatability conditions (closeness of the agreement between the results of successive measurements of the same solar irradiance and air temperature carried out under the same conditions of measurement) and reproducibility (closeness of the agreement between the results of measurements of the same solar irradiation and air temperature carried out under changed conditions of measurement). Numerous experimental tests were carried out and allowed the validation of the proposed concepts.

Copper zinc tin selenide (Cu2ZnSnSe4 or CZTSe) is a quaternary compound semiconductor material that has attained more and more attention for thin film photovoltaic applications. CZTSe is only comprised of abundant and non-toxic elements. People have concerns about availability and cost of indium from CIGS and tellurium from CdTe, also about cadmium’s toxicity. These concerns have promoted CZTSe as an alternative thin film solar cell material. The major issues about CZTSe absorber fabrication are: tin loss during selenization process and existence of secondary phases. Recent improvements of CZTSe absorber have increased the efficiency of CZTSe thin film solar cell to 9.7% in laboratory, and this was accomplished by using H2Se as selenium source in a “two-stage” process. [1] However “one-stage” vacuum co-evaporation technique is still the most popular technique for CZTSe thin-film solar cells fabrication. In this research, Cu2ZnSnSe4 thin-film solar cells have been fabricated by using a two-step rapid thermal selenization process. The first step selenization is operated at 375℃, a relatively low annealing temperature, which helps avoiding the most common issue of tin loss. The second step selenization is carried out at a higher annealing temperature, 400℃ to 500℃, at where the formation of CZTSe quaternary compound can be completed, and fewer secondary phases remain in the CZTSe absorber bulk. A specially designed metallic precursor stacks deposition order has been developed to inhibit tin loss and zinc loss during selenization. Vacuum co-evaporation technique is not feasible to mass production, due to facility difficulty and bad uniformity. And H2Se is toxic and dangerous. We have developed these metallic precursor stacks vacuum deposition process and two-step selenium vapor selenization process. We believe this technique is more suitable for potential mass production in future. The properties of CZTSe thin-films and the performance of CZTSe thin-film solar cells have been characterized using techniques, including J-V, Raman spectroscopy, spectral response, and SEM/EDS. The best performance CZTSe thin-film solar cell that have been accomplished, has an open circuit voltage of 0.42 volt, shirt circuit current densities of 14.5 mA/cm2, fill factor of 47%, and efficiency of 2.86%.

Ph.D. / A one-dimensional numerical simulation of photovoltaic (PV) cells has been written, and has been designated RAUPV2. An algorithm for determining the optical generation rate profile, taking into account multiple internal reflections in a multilayer cell has been developed. A method which enables realistic boundary values to be calculated, using RAUPV2 itself, has been developed. This method allows all three boundary values (', Fn and Fp) at each surface, to be determined, without the need to specify any additional input parameters. A comprehensive set of input parameters for aSi:H PV cells has been established, in consultation with the literature. Dangling-bond theory has been described and input parameters for dangling-bond defects have been presented. The effect of surface states in the p-layer on the contact potential at the TCO/p interface has been investigated. It was found that there is an intimate relationship between the contact potential and the parameters pertaining to the surface states. A simple method has been demonstrated, which has allowed RAUPV2 to reproduce the J-V curve of an existing aSi:H PV cell. The method requires that only the dangling-bond concentration in the i-layer and the contact potential at the Sn02/P interface needs to be adjusted. Once the J- V curve had been generated, the simulation results were used to characterise the empirical cell, in both thermodynamic- and steady-state equilibrium. This simulated cell was designated the realistic cell. The effect of asymmetries in the input parameters, under carrier band mobility interchange, on the performance of p-i-n cells has been investigated. The results indicate that, while asymmetries in the gap state distributions do give rise to asymmetrical behaviour in the J- V curve, the effect is slight, and it is the positional asymmetry of the optical generation profile that is mostly responsible for the observed asymmetry in the J- V curve under mobility interchange. An investigation of the limiting carrier effect has led to the conclusion that, in a p-i-n aSi:H cell under forward bias, the electron is the limiting carrier. This has been explained by appealing to the form of the optical generation profile, since most electron-hole pairs (EHPs) are generated near the front of the cell, and it is electrons that must be collected at the back contact. Investigations of the n-i-p aSi:H cell, under forward bias, have shown the hole to be the limiting carrier. It was found that the introduction of positional symmetry into the optical generation rate profile greatly reduced the limiting carrier effect, and it was concluded that the limiting carrier effect arises due to the asymmetries in the material parameters of the cell, particularly the _ positional asymmetry of the optical generation profile. It was observed that the nature of the optical generation profile actually plays an important role in determining the identity of the limiting carrier, in a p-i-n cell. The same effect was not observed in the n-i-p cell. The effective carrier collection length has been defined, and it was seen that the limiting carrier possesses the larger effective collection length. The effect of boron and phosphorous profiling of the i-layer was studied. It was found that boron profiling led to a decrease in cell performance, while phosphorous profiling improved cell performance. It was found that there was a P concentration at which cell performance peaked. The dependence of the spectral response of the realistic cell on device length L, was investigated, showing a general improvement in the spectral response as L was decreased. The spectral response has been interpreted in a novel way. It was assumed that the form of the monochromatic optical generation profiles in the vicinity of the peak in the spectral response represented optimal generation profiles. These profiles were subjected to a linear transformation, such that their form was preserved but that their integrated value was the same as that of the realistic optical generation profile, under global AM1.5 illumination. Using these transformed optical generation profiles, J- V curves were obtained. The maximum power output PM of these J- V curves was seen to exhibit a maximum some 17% greater than that of the realistic cell with a realistic optical generation profile. The spectral response of the phosphorous profiled cell was obtained. In a manner similar to that for the non-P profiled cell, the optimal generation profile was found. The PM for this profile was found to be 7.86mWcm -2 , considerably larger than the 5.60mWcm-2 for the phosphorous profiled cell with a realistic optical generation profile. The effect on the simulation output of variations in numerous dangling-bond defect input parameters has been investigated. It was found that the energy position and concentration of the doped layer defects need not be known to a high degree of precision. On the other hand, it was found that the energy position of the i-layer defects, the standard deviation of the defect distributions, and the defect carrier capture cross-sections, do need to be known with certainty.

M.Sc. / As environmental and energy resource concerns have increased, greater emphasis has been placed on development of renewable energy resources such as photovoltaic electric generators. CuInSe 2/ZnO heterojunction solar cells are currently one of the most promising technologies to produce economically viable, clean electrical energy. The reaction of metallic alloys containing copper and indium to a selenium-containing atmosphere is by far the most promising industrial process. In this study ; copper-indium metallic precursors were prepared by electron-beam evaporation. The selenization process was conducted in vacuum in elemental Se vapour and in the presence of a H 2Se/Ar gas mixture at atmospheric pressure. Attention was given to the optimization of the structural features of the metallic alloys as well as the selenization parameters. Structural analysis revealed that the number of multilayers in , the precursor stack significantly influence the morphological features of the absorber films after selenization. The reaction temperature and reaction periods during the selenization process critically influenced the reaction kinetics of metallic phases. In the case of selenization in elemental Se vapour, temperatures as high as 550°C were required to convert the metallic alloys into fully reacted semiconductor thin films. Selenization in the presence of H2Se gas was more reactive and temperatures around 450°C resulted in the complete formation of CuInSe2. In the majority of cases, traces of CuSe were detected in the bulk of the material by XRD studies. The presence of the Cu-rich binary phases rendered solar cell devices useless. After removal of these detrimental segregated phases by KCN etching, glass/Mo/CuInSe2/CdS/ZnO solar cell devices reached conversion efficiencies around 8%.

Ph.D. / The reaction of direct current (DC) magnetron sputtered metallic CuIn and CuInGa alloys to a reactive H2Se/Ar/H2S gaseous atmosphere is an attractive industrial production process to produce Cu-based chalcopyrite absorber films for applications in high efficiency photovoltaic modules. This deposition process is generally referred to as a two-step deposition technology. However, the obvious technological advantages of this deposition technology are overshadowed by growth-related anomalies, such as the separation or at least partial separation of the ternary phases (i.e. CuInSe2, CuGaSe2 and CuInS2) during the high temperature chalcogenization. This in turn prevents the effective band-gap widening of the semiconductor alloys in order to achieve open-circuit voltages in excess of 600mV, which is a critical prerequisite for the optimal performance of thin film solar modules. Against this background, a detailed study was undertaken in order to understand the formation kinetics of quaternary CuIn(Se,S)2 and pentenary Cu(In,Ga)(Se,S)2 alloys deposited with a reproducible two-step growth technology. The main objective of this study was to optimize a complex set of experimental parameters in order to deposit homogenous alloys in which the band-gap value of the resulting semiconductor film could be modified in order to maximize the operating parameters of photovoltaic devices. This was achieved by the homogenous incorporation of S and/or Ga into the chalcopyrite lattice, resulting in shrinkage of the lattice parameters and hence increase in band-gap value Eg. However, the substitution of In with Ga and Se with S proved to be a complex process. It was, for example, observed that separation or at least partial separation of the ternary phases already occurs during the chemical reaction between the hydrogen selenides (H2Se) gas and the metallic precursors. Detailed studies indicated that this phenomenon was strongly related to the selenization parameters (e.g. reactive gas concentration, and reaction temperature and time) as well as the Cu/(In + Ga) atomic ratio. In optimized processes, the metallic precursor films were partially selenized in order to produce at least one partially reacted Cu-III-VI2 ternary alloy and group Cu-VI and III-VI binary phases. The partially selenized alloys were subsequently sulphurized under optimal thermal conditions in a H2S:Ar gas mixture to produce homogeneous single-phase quaternary and pentenary chalcopyrite alloys. X-ray diffraction (XRD) studies revealed that the lattice parameters of the chalcopyrite lattice decreased linearly with the incorporation of S and/or Ga, according to the predictions of Vegard’s law. Gracing incidence x-ray diffraction (GIXRD) studies on the compound semiconductors revealed that the lattice parameters remained virtually constant through the entire depth of the layer. Optical studies revealed a shift in the band-gap value of the absorber films as function of the S concentration. The band-gap of the absorber films could be varied between 0.99 and 1.35eV by controlling the S/Se anion ratio during the diffusion process, while maintaining the Ga/III atomic ratio constant at 0.25. Solar cells were completed by chemical bath deposition (CBD) of CdS and radio frequency (RF) sputtered intrinsic and highly conductive ZnO films onto the absorber films. The cells were evaluated under standard A.M. 1.5 conditions. Devices manufactured from CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 based alloys demonstrated average open-circuit voltages (Voc) and short-circuit current densities (Jsc) values of 470 and 650 mV and 20 and 33 mA.cm-2, respectively. A plot of the open-circuit voltage as function of the band-gap revealed an experimental relationship of: Voc = (Eg/q – 0.6) mV for Eg < 1.3 eV. The fill factor (FF) values varied between 35 and 56% and device efficiencies () between 4 and 13%, depending on the S/Se anion ratio and Ga incorporation. The findings from the studies clearly indicated that a better understanding of the CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 formation process led to absorber material with improved material properties. It was also demonstrated that it is possible to produce a homogenous CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 absorber films with the scalable two-step deposition process.

Ph.D. / Thin film photovoltaic modules based on Cu(In,Ga)Se2 (CIGS) thin films possess attributes that enable them to compete effectively with silicon-based modules. These attributes are stability, high efficiency, and low material cost. A very promising industrial related process to produce the chalcopyrite absorber layers involves the selenization of metallic precursors. However, recent literature suggests that it is extremely difficult to incorporate an appreciable amount of gallium into the active region of the CIGS thin film. Regardless of its location in the precursor stack, gallium has been observed to segregate to the back of the film during the high temperature selenization step. Consequently, the resulting films are phase-segregated with CuGaSe2 near the Mo electrode and CuInSe2 at the film surface. In this study, the incorporation of gallium and sulfur into CuInSe2 thin films was systematically investigated to establish a scientific and engineering base for the fabrication of homogeneous CuIn(Se,S)2 and Cu(In,Ga)Se2 quaternary alloys with optimum band gap values between 1.1 and 1.2 eV. The selenization of seleniumcontaining (i.e. Cu/InSe, InSe/Cu and InSe/Cu/InSe) precursors in elemental Se vapour at temperatures around 550°C resulted in CuInSe2 thin films with superior structural properties. In an attempt to increase the band gap of these films, the selenium species were replaced by sulfur species during a solid-state diffusion process. Alternatively, gallium was introduced into the structure by replacing the InSe/Cu/InSe precursors with InSe/Cu/GaSe precursors. Important process parameters such as the deposition temperature of precursor elements, the selenization temperature in elemental Se vapour, as well as the concentration of gallium in the alloys were optimized during subsequent studies. From these systematic studies optimum experimental conditions were determined for the deposition of homogeneous Cu(In,Ga)Se2 thin films. The monophasic nature of the quaternary alloys was confirmed by XRD studies, revealing a shift in the lattice spacing due to the homogeneous incorporation of gallium into the chalcopyrite lattice. Completed solar cell devices revealed open-circuit voltages above 500mV, which confirmed the increase in the band gap value of the absorber films. / Professor V. Alberts