CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Dedicado à deposiÃÃo e caracterizaÃÃo de filmes finos de Sulfeto de CÃdmio e DiÃxido de TitÃnio para a aplicaÃÃo em cÃlulas solares fotovoltaicas. Cada filme foi depositado por um processo diferente. O reagente TiO2 da marca vetec, foi misturado com Ãcido clorÃdrico em soluÃÃo aquosa formando uma dispersÃo. Essa dispersÃo foi espalhada sobre o substrato de vidro e depois aquecida com uma chapa aquecedora. Depois de formado o filme, foram feitos MEV e EDX do mesmo. Para preparar o CdS foi necessÃrio um procedimento um pouco mais complexo, que à a deposiÃÃo por banho quÃmico, onde à feita uma mistura de reagentes e mergulhado o substrato nesta mistura. Ocorreram reaÃÃes quÃmicas cujo resultado foi a formaÃÃo do CdS, que ocorre em toda a superfÃcie do recipiente e do substrato imerso na soluÃÃo. As mesmas caracterizaÃÃes feitas no TiO2 foram feitas no CdS, ambos mostraram uma boa uniformidade, tambÃm foi observado que os filmes mostraram uma boa aderÃncia ao substrato. A fim de comprovar a aplicatividade dos filmes para fins fotovoltaicos, preparou-se um protÃtipo de cÃlula solar fotovoltaica, que foi colocada em contato com a luz solar para assim medir a corrente elÃtrica e a diferenÃa de potencial. TambÃm foram medidos os mesmos parÃmetros no escuro, para comparaÃÃo de resultados e comprovaÃÃo da geraÃÃo de energia elÃtrica atravÃs do contato com a luz. AtravÃs dos resultados destes testes, concluiu-se que os filmes apresentaram o efeito fotoelÃtrico, sendo assim, aplicÃveis em cÃlulas solares fotovoltaicas. / This work is dedicated to the deposition and characterization of thin films of cadmium sulfide and titanium dioxide for application in photovoltaic solar cells. Each film is deposited by a different process. The reagent TiO2 brand Vetec, was mixed with hydrochloric acid in aqueous solution forming a dispersion. This dispersion is spread on the glass substrate and then heated with a plate heater. After the deposit, were made SEM and EDX of the films. In order to prepare CdS a more complex process called chemical bath deposition was required, made of a mixture of reagents with the substrate immersed in it. Chemical reactions occurred which result was the formation of CdS, which occurs across the surface of the container and the substrate immersed in the solution. The same characterizations were carried out on TiO2 in CdS, showed in both good uniformity, was also observed that the films showed good adhesion to the substrate. In order to prove that films are applicable for photovoltaic energy conversion, a prototype of a solar photovoltaic cell was prepared, which was placed in contact with a type of light for measuring electrical parameters like the electric current and potential difference. We also measured the same parameters in the dark, for comparison of results and to prove power generation in contact with the light. The research tests provides evidence that films showed the photoelectric effect, therefore, applicable in photovoltaic solar cells.

Atualmente um dos principais objetivos na área de pesquisa tecnológica é o desenvolvimento de soluções em favor do Meio Ambiente. Este trabalho tem por objetivo demonstrar a reutilização e consequentemente o aumento da vida útil de uma bateria Chumbo-Ácido, comumente instaladas em veículos automóveis, bem como beneficiar locais e usuários remotos onde o investimento na instalação de linhas de transmissão se torna inviável geográfica e economicamente, utilizando a luz solar como fonte de energia. No entanto a parte mais suscetível a falhas são as próprias baterias, justamente pela vida útil delas serem pequenas (em torno de 3 anos para a bateria automotiva) em comparação com o restante do sistema. Considerando uma unidade que já foi usada anteriormente, a possibilidade de falhas é ainda maior. A fim de diagnosticar e evitar que uma simples bateria possa prejudicar o funcionamento do sistema como um todo, o projeto considera a geração de energia elétrica por células fotovoltaicas e também contempla um sistema microcontrolado para leitura de dados utilizando o microcontrolador ATmega/Arduino, leitura de corrente por sensores de efeito hall da Allegro Systems, relés nas baterias para abertura e fechamento delas no circuito e um sistema de alerta para o usuário final de qual bateria está em falha e que precisa ser reparada e/ou trocada. Esse projeto foi montado na Ilha dos Arvoredos SP, distante da costa continental em aproximadamente 2,0km. Foram instaladas células solares e um banco de baterias, a fim de estudar o comportamento das baterias. O programa pôde diagnosticar e isolar uma das baterias que estava apresentando defeito, a fim de se evitar que a mesma viesse a prejudicar o sistema como um todo. Por conta da dificuldade de locomoção imposta pela geografia, foi escolhido o cartão SD para o armazenamento dos dados obtidos pelo Arduino. Posteriormente os dados foram compilados e analisados. A partir dos resultados apresentados podemos concluir que é possível usar baterias novas e baterias usadas em um mesmo sistema, de tal forma que se alguma das baterias apresentar uma falha o sistema por si só isolará a unidade. / Actually one of the main goals in the technology research area is the development of solutions in accordance with our Environment. The objective of this work is to illustrate the reuse and consequently increase of the Lead-Acid Secondary Battery lifecycle, commonly installed in automotive vehicles, as well as to benefit remote areas and users, where the investment in a new electrical infrastructure is unfavorable geographically and economically, using sunlight as a feasible and available alternative solution. However, the most fragile part of the system are the batteries, due to their own short service life (approximately 3 years for the automotive battery), compared with the other equipment within the system. The chance to have a failure is even higher when using a unit which has been serviced before. In order to anticipate and avoid that a single faulty battery could bring the entire system down, the project consider using photovoltaic cells for electricity generation and also has a micro-controlled system for data reading using an ATmega/Arduino microcontroller, current readings using hall-effect sensors from Allegro Systems, relays on the batteries to open and close themselves in the circuit and an alarm system that indicates to the user which battery is faulty as well as needing repair and/or replacement. This project has been installed in Ilha dos Arvoredos SP, a small island with approximately 2.0km far from the coast. Solar cells and a battery string have been installed in order to study the behavior of the batteries. The programming could diagnose and isolate one of the batteries that has been having a failure, to avoid that this same single battery could cause a major failure on the entire system. Due to the restrictions imposed by the geography, the SD card has been chosen for the data storage obtained by Arduino board. Later on the data has been compiled as well as analyzed. The obtained data has shown that it is possible using old and new batteries in a same string, as long as the system will isolate the faulty battery if any of the batteries shows a failure.

Orientadores: Ana Flávia Nogueira, Teresa Dib Zambon Atvars / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-19T07:00:55Z (GMT). No. of bitstreams: 1 Alves_JoaoPaulodeCarvalho_M.pdf: 2190959 bytes, checksum: a321ebe05ad04c15ea1e77782b12c743 (MD5) Previous issue date: 2011 / Resumo: Células solares orgânicas apresentam-se como uma alternativa promissora para conversão de energia solar. Muitos desses dispositivos são produzidos pela mistura de um polímero condutor e um derivado fulereno. O polímero condutor atua como absorvedor de luz, doador de elétrons e transportador de buracos, enquanto o fulereno atua como transportador e aceitador de elétrons. Esses dispositivos destacam-se pela possibilidade de deposição em substratos flexíveis, transparência, diversidade em cores e uso de materiais recicláveis, além do baixo custo. No entanto, células solares orgânicas apresentam baixa mobilidade de carga e absorção em pequena faixa espectral da energia solar quando comparadas aos dispositivos fotovoltaicos baseados em semicondutores inorgânicos. A adição de CdSe ao sistema P3HT/PCBM promoveu o decréscimo na eficiência e fotocorrente dos dispositivos. Esses resultados são diferentes dos observados para o sistema PFT/PCBM, previamente reportado. A diferença observada para os dispositivos com os polímeros P3HT e PFT foram associados com as diferentes interações polímero-nanopartícula, como evidenciado pelas medidas de absorção e emissão e pelos espectros de RMN. A elevada concentração de tiofeno no P3HT pode contribuir fortemente na formação de um complexo entre polímero e CdSe e na desativação do processo de transferência de elétrons entre polímero e PCBM. Para investigar um possível efeito de morfologia pela introdução de CdSe ao sistema P3HT/PCBM, foram obtidas imagens de microscopia de força atômica e microscopia óptica. Há um aumento da rugosidade e tamanho de grãos do sistema com o acréscimo de nanopartículas de CdSe, que pode inibir o processo de separação de cargas e de formação de redes de percolação / Abstract: Organic solar cells are presented as a promising alternative for solar energy conversion. Many of these devices are produced by mixing a conductive polymer and a fullerene derivative. The conducting polymer acts as a light absorber, electron donor and hole transporter, while the fullerene acts as acceptor and electron shuttle. These devices call attention due to the possibility to produce flexible solar cells with high transparency and different colors, allied to the use of recyclable materials and low cost. However, organic solar cells have lower charge mobility and narrower spectral range absorption of solar energy compared to inorganic-based photovoltaic devices. The addition of CdSe to the P3HT/PCBM system promoted the decrease in efficiency and photocurrent of the devices. These results are different from those observed for the PFT/PCBM system, previously reported. The difference observed for the devices with P3HT and PFT was associated with different polymer-nanoparticle interactions, as evidenced by absorption and emission measurements. The high concentration of thiophene in P3HT contributes in the formation of a complex between polymer-CdSe and the deactivation of the electron transfer process between the polymer and PCBM. To investigate the possible contribution of a morphological effect induced by CdSe in P3HT/PCBM system, Atomic Force Microscopy (AFM) images were obtained. There is an increase of roughness and grain size of the system with the addition of CdSe nanoparticles, which can inhibit the charge separation process and formation of percolation networks / Mestrado / Quimica Inorganica / Mestre em Química

M.Sc. (Physics) / Amorphous silicon is one of the most promising materials for large area solar cells for terestrial photovoltaic applications. Unfortunately these cells suffer from two serious problems: the efficiencies drop when laboratory processes are scaled up and the cells degrade after some exposure to sunlight. The exact causes of these two problems are still unknown. In this project some aspects of the latter problem were investigated. The photo-degradation was investigated by illuminating films of a-Si:H with simulated sunlight for different periods of time and then thermally annealing them. The change in the optical properties were investigated with the aid of optical transmission spectroscopy. The films were also characterized by Fourier Transform Infra-Red (FTIR) spectroscopy. The change in the electrical properties of the intrinsic films was determined as function of temperature and total photon flux. No change in the optical properties could be detected. The illumination had-no effect on the FTIR measurements. It seems as if the hydrogen is not involved in the microscopic processes leading to the Staebler-Wronski Effect (SWE). The effect of the photo-degradation manifests itself in a drop in the the dark conductivity and photoconductivity over the total temperature range that was investigated. The observed phenomena are explained in terms of photo-induced deep levels in the gap. The Fermi level shifts to the middle of the gap due to these defect states, causing a drop in the free carrier concentration and conductivity. The measurements of photoconductivity as function of photon energy show that these defect levels increase the absorption coefficient in the long wavelength region, but they also decrease the lifetime of the photo-generated carriers. The photo-induced defects were investigated with the CPM-technique. It was found that the light introduced defects deep in the band gap. The concentration of the defects increases with illumination, but saturates after about 24 hours of illumination. The defects could be annealed almost completely. The microscopic processes causing the photo-degradation of α Si:H solar cells were investigated by comparing the different theoretical models explaining the SWE with the results obtained during this project.

Les travaux réalisés durant ces années de doctorat ont été axés sur la conception de fluorophores pour diverses applications en fluorescence ou dispositifs de conversion d’énergie. Ainsi, plusieurs composés de la famille des Bodipys et triazatruxène ont été synthétisés, caractérisés et étudiés. En fonction des modifications structurales apportées à ces molécules, il est possible d’obtenir un panel de composés possédant une gamme d’absorption et d’émission pouvant s’étendre de 500 à 800 nm. La modulation de ses propriétés optiques a un intérêt dans un grand nombre d’applications. Ainsi, divers Bodipys ont été synthétisés en vue d’une éventuelle application pour le marquage biologique ou bien servant de support à l’étude du transfert d’énergie intramoléculaire. Le fort pouvoir absorbant de ces composés a été mis à contribution pour la réalisation de cellules solaires organiques originales et performantes. / The work undertaken during this PhD was focused on the design of fluorophores for several applications in fluorescence or energy conversion device. Several compounds from the Bodipy and Triazatruxene families were synthesized, characterized and studied. By structural modifications brought to these molecules, it was possible to obtain a panel of compounds those posses a range of absorption and emission properties which extend from 500 to 800 nm. The modulation of these optical properties has an interest in a large number of applications and field of research. Several Bodipys were synthesized for potential application in biological labeling and specific energy transfer processes. The strong absorption power and dedicated redox properties of these compounds was exploited for the preparation of solar

Une approche mixte théorique/expérimentale a été utilisé pour analyser les composants semi-conducteurs des cellules solaires à boites quantiques, ainsi que les interfaces qui se forment entre eux. En ce qui concerne la partie théorique de cette thèse, tout d'abord on a identifié un protocole computationnel pour décrire les propriétés géométriques et électroniques du bulk et les surfaces de CdSe. Après, les nanoplaquettes CdSe de plusieurs épaisseurs et passivé par plusieurs ligands distincts ont été simulés. Ensuite, une hétéro-structure nanocristal - semi-conducteurs à large bande interdite a été modélisée, et ses propriétés structurelles, vibrationnelles et électroniques ont été calculées. Expérimentalement, des semi-conducteurs à large bande interdite sous le forme de nanobatôns, ainsi que des nanocristaux sous forme des nanoplaquettes et des boîtes quantiques CdSe ont été synthétisées. Les nanobatôns ont été sensibilisés avec des nanocristaux CdSe préparés ex situ et in situ. Ces hétérostructures semi-conducteurs ainsi préparées ont été caractérisées par spectroscopie d'absorption UV-VIS et Raman. Enfin, des cellules solaires incorporant ces systèmes ont été fabriquées et testées. L'approche combiné expérimentale/théorique qu'on a utilisée a rendu possible de contre-valider la capacité des méthodes expérimentales et théoriques pour caractériser les systèmes semi-conducteurs étudiées lors de cette thèse. De plus, on a pu établir des indications générales pour la sélection des composants pour ces dispositifs. Cette approche mixte peut être étendu pour étudier des hétérostructures semi-conducteurs dans une vaste gamme des applications optoélectroniques. / A mixed theoretical/experimental approach was used to analyze the semiconductor components of quantum dot sensitized solar cells and the interfaces formed between them. We first identified a computational protocol that accurately and efficiently describes the bulk and surface geometrical and electronic properties of CdSe. Then, we simulated CdSe nanoplatelets of various thicknesses, passivated by different ligands. Next, a model of the sensitizer - wide band gap semiconductor heterostructure was built and its structural, vibrational and electronic properties were calculated. In the meantime, computational results were compared to experimental data. Wide band gap semiconductors (WBSC) in the form of nanorods and sensitizer nanocrystals (CdSe nanoplatelets and quantum dots) were synthesized. The WBSC substrates were sensitized both by ex situ and in situ grown CdSe QDs. The as-prepared semiconductor systems were characterized by UV-VIS absorption and Raman spectroscopy. Finally, solar cells based on these heterostructures were fabricated and tested. The applied combined theoretical/experimental approach made it possible to cross-validate the capacity of computational and experimental methods for the characterization of the semiconductor systems studied in this thesis. Moreover, general guidelines for the screening of QDSC components could be drawn from the obtained results. The here proposed mixed theoretical/experimental approach can be extended to other semiconductor heterostructures in a wide variety of optoelectronic applications, and it could contribute to a better understanding of the working principle of these devices and improve their performance.

Abstract Printed electronics offer unique possibilities for the development of devices and manufacturing methods. A prime example of printed electronics where the production volume can be significantly increased are solution-processed organic solar cells. Roll-to-roll (R2R) technology has made it possible to print solar cells almost as fast as newspaper. Unfortunately, the performance of printed devices depends strongly on film morphology, which is affected by the behaviour of the used ink on the confining surface - wetting. Key parameters that influence the wetting behaviour include surface energy, ink formulation, surface roughness, solvent properties, processing temperature and pre/post-treatments (heat, acid or plasma) and chemical heterogeneity. Importantly, a precise control of wetting and, consequently, film morphology is emphasized by many authors as an important factor for the commercialization of printed solar cells. This research focuses on measuring and analysing the influence of substrate processing temperature as well as plasma and UV pre-treatments on the wettability of various inks and substrates used in Organic Solar Cell (OSC) fabrication. It also explores the application of interesting novel materials, such as nanocellulose, in solar cell manufacture. The main tool applied here is the contact angle measurement method, since it is commonly used to obtain quantitative data describing the behaviour of ink droplets on substrate surfaces. Chief among the achieved results is the finding that the three factors mentioned above significantly influence ink-substrate interactions. Therefore, manipulation of plasma and UV treatments as well as substrate processing temperature, allow us to control wetting properties and, in consequence, the printing process. Another important result shows that the degree of control is strongly dependent on ink formulation and material composition and must, therefore, be taken into account in process development. These findings will contribute to a faster development of printed solar cells and their manufacturing conditions and requirements. / Tiivistelmä Painettava elektroniikka tarjoaa uusia mahdollisuuksia elektronisten laitteiden ja niiden valmistusmenetelmien kehittämiseen. Liuoskäsitellyt orgaaniset aurinkokennot ovat hyvä esimerkki painetun elektroniikan tuotteesta, jonka tuotantomäärää on voitu kasvattaa merkittävästi. Rullalta rullalle (engl. Roll-to-roll, R2R) -menetelmän avulla aurinkokennoja voidaan painaa lähes samalla nopeudella kuin sanomalehteä. Painettujen laitteiden suorituskyky riippuu suuresti tuotetun kalvon morfologiasta, johon vaikuttavat tuotantoprosessissa käytettyjen materiaalien kostumisominaisuudet. Tärkeimmät kostumiskäyttäytymiseen vaikuttavat parametrit ovat pintaenergia, pinnan karheus, musteen koostumus, liuotinominaisuudet, käsittelylämpötila, esi- ja jälkikäsittely (lämpö, happo tai plasma) sekä kemiallinen heterogeenisyys. Kostumisen, ja sitä kautta kalvon morfologian, tarkka säätely on tärkeää painettujen aurinkokennojen kaupallisen hyödyntämisen kannalta. Tässä väitöskirjatyössä mitataan ja analysoidaan käsittelylämpötilan sekä plasma- ja UV-esikäsittelyiden vaikutuksia orgaanisten aurinkokennojen valmistuksessa käytettyjen musteiden ja alustojen kostumisominaisuuksiin sekä tarkastellaan aurinkokennoliuoksissa käytettäviä uusia, mielenkiintoisia materiaaleja, kuten nanoselluloosaa. Työssä eniten hyödynnetty menetelmä on kontaktikulman mittaus, joka on yleisesti käytetty tapa hankkia kvantitatiivista tietoa mustepisaroiden käyttäytymisestä erilaisilla pinnoilla. Keskeisin saavutettu tutkimustulos on se, että kaikilla yllämainituilla kolmella käsittelyllä on huomattava merkitys musteen ja alustan vuorovaikutuksiin. Näin ollen plasma- ja UV-käsittelyillä sekä alustan käsittelylämpötilan säätelyllä voidaan hallita kostumisominaisuuksia ja sitä kautta koko painatusprosessia. Toinen tärkeä löydös on, että musteen koostumus ja alustan materiaali vaikuttavat siihen, kuinka voimakkaasti kostumista voidaan hallita. Näin ollen ne täytyy ottaa huomioon painatusprosessin suunnittelussa. Työssä saavutettuja tuloksia voidaan käyttää painettujen aurinkokennojen sekä niiden tuotantomenetelmien kehittämiseen.

Philosophiae Doctor - PhD / The first report of a functioning photo-electrochemical solar cell in 1991 attracted a lot of interest from scientists and industrial groups. From an industrial point of view these so-called dye-sensitised solar cells (DSCs) offered the promise of moderate efficiency devices at ultra-low costs, owing to simple processing methods and the use of inexpensive materials. From an academic viewpoint, DSCs raised important scientific questions around the fundamental processes governing their operation and how these processes influence the photon-to-electron conversion efficiency of the cell. Major successes have since been achieved in understanding these processes, however the conversion efficiency of the best manufactured DSCs remains around 11%, significantly lower than that of their silicon photovoltaic counterparts. In traditional DSCs, charge generation is achieved by ultrafast electron injection from a photo-excited ruthenium-based dye molecule into the conduction band of a film of TiO₂ nanoparticles, subsequent dye regeneration by an I⁻ /I⁻₃ containing redox electrolyte and finally hole transportation to a platinum-coated counter electrode. The low DSC efficiencies are attributed to scattering of electrons at the interface between two TiO₂ nanoparticles leading to recombination with holes present in the redox electrolyte. Recent studies have shown that the application of films of highly ordered TiO₂ nanotubes instead of nanoparticles has the potential to improve the overall conversion efficiency of the cell. This is ascribed to the one-dimensional nature of nanotubes, which provides a linear transportation route for electrons generated during operation of the DSC. As a result the recombination probability of the electrons with nearby holes in the device is decreased. This work investigated the synthesis of Al₂O₃-coated TiO₂ nanotubes via the anodisation technique for application in DSCs. TiO₂ nanotube arrays with an average length of 15 μm, diameter of 50 nm and wall thickness of 15 nm were synthesised via anodisation using an organic neutral electrolyte consisting of 2 M H₂O + 0.15 M NH₄F + ethylene glycol (EG) at an applied voltage of 60 V for 6 hours. In addition, scanning electron microscope (SEM) micrographs showed that anodisation at these conditions yields nanotubes with smooth walls and hexagonally shaped, closed bottoms. X-ray diffraction (XRD) patterns revealed that the as-anodised nanotubes were amorphous and as such were annealed at 450 °C for 2 hours in air at atmospheric pressure, which yielded crystalline anatase TiO₂ nanotubes. Highresolution transmission electron microscope (TEM) images revealed that the nanotube walls comprised of individual nano-sized TiO₂ crystallites. Photoluminescence (PL) spectroscopy showed that the optical properties, especially the bandgap of the TiO₂ nanotubes are dependent on the crystallinity, which in turn was dependent on the structural characteristics, such as the wall thickness, diameter and length. The PL measurements were supplemented by Raman spectra, which revealed an increased in the quantum confinement of the optical phonon modes of the nanotubes synthesised at low anodisation voltages, consequently yielding a larger bandgap The annealed nanotubes were then coated with a thin layer of alumina (Al₂O₃) using a simple sol-gel dip coating method, effectively used to coat films of nanoparticles. Atomic force microscopy (AFM) showed that the average nanotube diameter increased post sol-gel deposition, which suggests that the nanotubes are coated with a layer of Al₂O₃. This was confirmed with HR-TEM, in conjunction with selected area electron diffraction (SAED) and XRD analyses, which showed the coating of the nanotube walls with a thin layer of amorphous Al₂O₃ with a thickness between 4 and 7 nm. Ultraviolet-visible (UVvis) absorbance spectra showed that the dye-adsorption ability of the nanotubes are enhanced by the Al₂O₃ coating and hence is a viable material for solar cell application. Upon application in the DSC, it was found by means of photo-current density – voltage (I – V) measurements that a DSC fabricated with a 15 μm thick layer of bare TiO₂ nanotubes has a photon-to-light conversion efficiency of 4.56%, which increased to 4.88% after coating the nanotubes with a layer of alumina. However, these devices had poorer conversion efficiencies than bare and Al₂O₃-coated TiO₂ nanoparticle based DSCs, which boasted with efficiencies of 6.54 and 7.26%, respectively. The low efficiencies of the TiO₂ nanotube based DSCs are ascribed to the low surface area of the layer of nanotubes, which yielded low photocurrent densities. Electrochemical impedance spectroscopy (EIS) showed that the electron lifetime in the alumina coated nanotubes are almost 20 times greater than in a bare layer of nanoparticles. In addition, it was also found that the charge transfer resistance at the interface of the TiO₂/dye/electrolyte is the lowest for an Al₂O₃-coated TiO₂ layer.

Cu2ZnSnSSe4 (CZTSSe) est un matériau prometteur comme absorbant de cellules photovoltaïques. Le développement à grande échelle de cellules solaires CZTSSe est conditionné au développement de procédés bas coût et soucieux de l'environnement. Dans ce contexte, le développement de films de CZTSSe à partir d'encres tout aqueuses de nanoparticules de CZTS constitue un challenge intéressant. Une stratégie haute température en présence d'un agent texturant gaz a été définie pour synthétiser des nanocristaux de CZTS présentant des surfaces polaires. Notre procédé agent texturant gaz met en œuvre la formation simultanée de nucléis de CZTS et de bulles de gaz. Nous montrons que la production en conditions de forte sursaturation d'une très forte concentration de nucléis de CZTS en association à un très grand nombre de petites bulles de gaz représente les conditions optimales de formation de nanocristaux. Par une étude électrocinétique, une condensation régulée par la taille de l'ion alcalin est observée dans la série des alcalins Li+ < Na+ < K+ < Rb+ < Cs+, démontrant la stabilité chimique des surfaces de Cu2ZnSnS4 en dispersion toute aqueuse. Par mise en œuvre des dispersions tout aqueuses, nous avons réalisé l'acquisition de données de base permettant de produire une preuve de concept de la formation d'un film sans fissures. Un autre point important à considérer lors de l'utilisation de matières premières bas coût est l'élimination des impuretés inhibitrices de la croissance des grains. Un profil spécifique de recuit des films est proposé mettant en œuvre une purification haute température pour l'élimination du carbone. En effet, notre stratégie met en œuvre la décomposition des domaines amorphes en carbone sp2 qui est ultérieurement éliminé via la formation de CSe2 gazeux. Finalement, des cellules solaires ont été fabriquées avec succès à partir d'encres tout aqueuses avec des rendements de conversion préliminaires jusqu'à 2,6 %. / Recently more attention is devoted to Cu2ZnSnS4 (CZTSSe) for photovoltaic applications due to their non-toxic, earth-abundant components and good optoelectronic properties. Large scale fabrication of CZTSSe solar cells will rely on the development of low-cost and environmentally-friendly approach. In this context, development of CZTSSe films from all-aqueous CZTS nanocrystals inks represents an interesting challenge. A high temperature, gas-templating strategy has been defined to synthesize highly crystallized CZTS nanocrystals displaying polar surfaces. Our gas-templating process involves the simultaneous formation of CZTS nucleis and gas bubbles. We demonstrate that production of a high rate of small gas bubbles, as well as a high concentration of nucleis, depict optimal conditions for nanocrystal synthesis. By an electrokinetic investigation, a condensation regulation by the alkali ion size is observed in the alkali series Li+ < Na+ < K+ < Rb+ < Cs+, demonstrating the chemical stability of CZTS surfaces in aqueous basic dispersions. By using all-aqueous chalcogenide nanocrystals dispersions, we determined a critical cracking thickness of 250 nm and an average thickness of 100 nm to fabricate micron crack-free films using a multilayer procedure. Having in mind these results, we give the proof of concept of crack-free film formation from all aqueous CZTS nanocrystals inks. Another important consideration, when employing low-cost materials, is the removal of impurities, inhibitors of grain growth. A specific annealing profile is proposed involving a high temperature purification step in order to remove carbon. Indeed, our strategy involves the decomposition of amorphous domains into sp2 carbon which will be further removed via the CSe2gas formation. Finally, CZTSSe solar cells are successfully fabricated from all-aqueous CZTS inks with preliminary devices efficiencies up of 2.6%.

To mitigate the risk for devastating climate changes, there is an urgent need to change the energy production from the current fossil based to renewable sources. Solar cells will contribute to an increasing share of the future energy systems. Today silicon solar cells dominate the market but printed organic solar cells are promising alternatives in terms of cost, flexibility, possibilities for building integrations and energy payback times. Printing enables roll-to-roll processing that is quick and renders huge volumes. Thus, also characterization and quality control must be fast. Recent tests have been performed showing that a LED array with amplitude modulated LEDs can be used to provide photocurrent images of modules with series connected sub cells in-line during manufacturing. The purpose of this thesis work is to further evaluate and develop this LED array characterization technique focusing on contact methods and signal interpretation. Two modes were examined; a contact mode and a capacitive contact-less mode. Both modes gave comparable results and indicated strong variations in performance of sub cells in the measured modules. Other methods to address individual cells also showed similar behavior. However, by manually adding extra contact points, current-voltage curves could be measured on the individual sub cells in the modules. Extraction of photocurrents were similar, but the parallel resistances varied strongly between the cells in the module. Increasing the frequency of the LEDs resulted in less variations. Calculations indicated that this frequency dependence could be used to separate the photocurrent generation and parallel resistance in the sub cells.