This work studies the subject of perovskite solar cells. The structure of perovskites is described along with a portion of photovoltaics history that led to the employment of perovskites as absorpsion layers. Further, methods of measurement for solar cells such as impedance spectroscopy, photospectroscopy and load characteristics are summarized. Lastly there is a description of already done analytics of perovskite solar cells with the summary of the results. In the practical part, there are measurements made to find out any effect of cell topology or light source wavelength on the cell performance.

En esta tesis se centra en el estudio de capas delgadas basadas en óxido de zinc (ZnO) para aplicaciones fotovoltaicas, en concreto células solares sensibilizadas con colorante (DSSC). Se optimizaron los parámetros de crecimiento de estas nanoestructuras hibridas depositadas mediante la técnica de electrodeposición catódica para posteriormente desarrollar un dispositivo eficiente para la conversión de la luz. OBJETIVOS Los objetivos principales de la tesis son: - Establecer las condiciones de crecimiento de las películas híbridas de ZnO/colorante mediante su estudio morfológico, estructural, óptico y eléctrico. - Verificar la incorporación de diferentes colorantes como Eosin-Y, Fthalociania de cobre (Ts-CuPc) y N719 en la estructura del ZnO. - Implementación de una celda DSCC basada en estas películas híbridas para la conversión de la energía mediante el cálculo de eficiencia. ELEMENTOS DE LA METODOLOGÍA La técnica de depósito utilizada para la obtención de estos materiales híbridos es la electrodeposición catódica. Para el estudio y la optimización de estas películas se utilizaron diferentes técnicas de caracterización física mediante SEM, AFM, XRD, transmitancia, fotocorriente, etc. Y finalmente, estas películas se integraron en dispositivos DSSC. RESULTADOS LOGRADOS Los resultados obtenidos fueron los siguientes: - Optimización y caracterización del crecimiento de la película delgada de ZnO. Se observo que la estructura hexagonal del ZnO es modificable y altamente dependiente de la concentración tanto de los precursores como del disolvente en la disolución. Las películas con mejores propiedades cristalinas se obtuvieron a una temperatura de depósito de 80°C y a un potencial de -0,9 V. - Optimización y caracterización del crecimiento de películas delgadas de ZnO/híbridas usando distintos colorantes: Eosin-Y, Ts-CuPc y N719. Las propiedades eléctricas y físicas se pueden modificar variando las concentraciones de los colorantes. En el caso del / Moya Forero, MM. (2012). PREPARACIÓN ELECTROQUÍMICA DE CAPAS NANOESTRUCTURADAS DE ZnO PARA APLICACIONES FOTOVOLTAICA [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/17322

Mesoporous semiconductors such as TiO2 nanoparticles, as well as transparent conducting oxides (TCOs) such as indium tin oxide films are typically employed for setting up the photo-electrode module in variety of photoelectrochemical cells including Dye-Sensitized Solar Cells (DSSCs). In order to exhibit a high performance efficiency, the photo-electrodes in such applications are required to be able to harvest the light and transport the generated electrons effectively. Accordingly mesoporous layers with high values of surface area and well-established pore structure along with highly transparent and conductive TCOs are deposited on suitable substrates through the physical or chemical vapor deposition methods. The processing facilities and materials required to fabricate such high-quality devices with high values of efficiency are complicated and expensive, whereas devices of lower quality do not fulfill the demands. This issue is of particular importance regarding the energy production and developing the solar cell technologies, as it is considered by the concept of “cost per watt”. Thus, a great deal of effort is being carried out globally to enhance the efficiency of affordably-produced solar cells such as low-cost DSSCs. Utilizing the wet chemical techniques such as sol-gel method which provide a considerably more affordable route to synthesize nanoparticles and deposit thin films without the need of applying high temperature or vacuum condition is a widely-used approach to decrease the processing expenses. However, to achieve an acceptable cost-per-watt ratio requires enhancing the obtained efficiency value as well, and therefore, modifying the processing procedures to improve the required features of the products are highly encouraged. This thesis focuses on two individual activities: synthesis of TiO2 nanoparticles, and also thin film deposition of a promising TCO called aluminum-doped zinc oxide (AZO); both obtained through the sol-gel route that is modified to contribute to nanostructures with suitable features for application in photoelectrochemical devices such as DSSC. In the first part, mesoporous anatase nanoparticles were synthesized through the surfactant-mediated sol–gel route. Through changing the refluxing time and water-to-surfactant molar ratio, as-prepared nanocrystals of high density and large and narrowly-distributed pore sizes were obtained, displaying surface area values up to 240 m2·g-1, much higher than the reported values for commercial TiO2-based catalysts. In the second part, sol–gel dip–coating of ZnO thin films doped with 2 at.% of aluminium ions was carried out. By altering the hydrolysis reaction and changing the thermal treatment procedure, thin films of highly c-axis preferred orientation were obtained with optical transmittance of around 80% and resistivity values down to 6 – 15 mΩ·cm, corresponding to sheet resistance of around Rsh ~ 500 Ω/sq. The obtained conductivity values, even though one order magnitude lower than those reported for the AZO thin film prepared via expensive techniques, are in the suitable range to improve the cost per watt ratio in applications such as inkjet printing of low-cost printed electronics and more affordable DSSC devices.

Ce travail a consisté à élaborer de nouveaux verres moléculaires transporteurs de trou dérivés du carbazole pour remplacer le spiro-OMeTAD (matériau de référence) dans les cellules solaires hybrides à colorant tout solide. Nous avons synthétisé différents dérivés du carbazole 3, 6, 9 substitués, établi leurs principales propriétés physico-chimiques et les avons utilisés en DSSC solide. Nous avons mis en évidence l'intérêt de greffer des groupements bis(4-méthoxyphényl)amines en positions 3, 6 et des aryles en position 9 du carbazole pour obtenir des matériaux performants. Finalement, cette structure type établie a permis de développer un concept innovant de synthèse de dérivés de carbazole ouvrant la voie à l'élaboration d'une large famille de verres moléculaires et permettant la préparation aisée de structures complexes performantes dans les DSSC solide. Nos meilleurs matériaux ont donné, en dispositifs sans optimisation, des performances comparables à celles du spiro-OMeTAD permettant d'entrevoir à terme la préparation de dispositifs à sensibilisateur pérovskite de rendements supérieurs à 15% / The aim ot this work has been to prepare new hole transporting molecular glasses based on carbazole moieties as an alternative to spiro-OMeTAD (standard material) in solid state dye sentitized solar cells (ssDSSC). We have synthesized several 3, 6, 9 substituted carbazole derivatives and have established their physical and chemical properties prior using them in photovoltaic devices. We have demonstrated the interest of grafting functional groups as bis(4-methoxyphenyl)amines on 3, 6 positions and aryl substitutes on the 9 position of carbazole to obtain efficient materials. Finally, this latter chemical structure has been used as a building block to develop an innovative concept of synthesis of carbazole based materials, smoothing the way to easy synthesis of a wide family of efficient molecular glasses for ssDSSC. Our best materials exhibit similar power conversion efficiency compare to the standard spiro-OMeTAD. According to these preliminary results, we expect reaching power conversion efficiencies over 15% with our carbazole based hole transporting materials associated with peroskite sensitizer.

Photon upconversion by sensitized triplet–triplet annihilation (UC-STTA) is a photophysical process that facilitates the conversion of two low-energy photons into a single high-energy photon. A low-energy photon is absorbed by a sensitizer molecule that produces a triplet excited state which is transferred to an emitter molecule. When two emitter triplet states encounter each other, TTA can take place to produce a singlet excited state which decays by emission of a high-energy (upconverted) photon. While traditional single-threshold dye-sensitized solar cells (DSSCs) have a maximum efficiency limit of ca. 30%, it has been predicted theoretically that implementation of UC-STTA in DSSCs could increase that efficiency to more than 40%. A possible way to implement UC-STTA into DSSCs, would be to replace the standard sensi- tized nanostructured TiO2 photoanodes by upconverting ones loaded with emitter molecules. Following TTA, the excited emitter molecule would be quenched by injection of a high-energy electron into the conduction band of the TiO2. To explore the practical aspects of this strategy for a highly efficient DSSC, in this thesis UC-STTA is studied in model systems based on nanostructured ZrO2 films. These ZrO2 films are a good proxy for the TiO2 films used in DSSCs, and allow for relatively easy optimization and study of UC-STTA by allowing measurements of the upconverted photons without the complications of electron injection into the film. Herein it is experimentally proven that UC-STTA is viable on nanostructured metal oxide films under non-coherent irradiation with intensities comparable to sunlight. Two different system architectures are studied, differing in the position of the molecular components involved in the UC-STTA mechanism. Both architectures have the emitter molecules adsorbed onto the ZrO2 surface, but the sensitizers are positioned either in solution around the nanostructure, or co-adsorbed with the emitters onto the ZrO2 surface. A set of challenges in the study and optimization of the UC-STTA process is identified for each type of system. Proposals are also given for how to further improve the understanding and UC-STTA optimization of these systems toward application in DSSCs to overcome the present solar energy conversion efficiency limit.

Title from first page of PDF document. Includes bibliographical references (p. 154-156).

abstract: Alternative energy technologies must become more cost effective to achieve grid parity with fossil fuels. Dye sensitized solar cells (DSSCs) are an innovative third generation photovoltaic technology, which is demonstrating tremendous potential to become a revolutionary technology due to recent breakthroughs in cost of fabrication. The study here focused on quality improvement measures undertaken to improve fabrication of DSSCs and enhance process efficiency and effectiveness. Several quality improvement methods were implemented to optimize the seven step individual DSSC fabrication processes. Lean Manufacturing's 5S method successfully increased efficiency in all of the processes. Six Sigma's DMAIC methodology was used to identify and eliminate each of the root causes of defects in the critical titanium dioxide deposition process. These optimizations resulted with the following significant improvements in the production process: 1. fabrication time of the DSSCs was reduced by 54 %; 2. fabrication procedures were improved to the extent that all critical defects in the process were eliminated; 3. the quantity of functioning DSSCs fabricated was increased from 17 % to 90 %. / Dissertation/Thesis / M.S.Tech Technology 2012

Solar cells are designed to transform the optical energy into electrical energy. Using solar energy is the best way for humans to solve the energy shortage problem. Dye sensitized solar cell(DSSC) has a low cost and helps people to obtain the solar energy expediently. The DSSC is based on nano structured TiO2 ; and dye molecules help the particles of TiO2 to absorb more photons. Hence DSSC has higher efficiency than SC(solar cell without dye). This thesis elaborates and analyzes the dye which is sensitized to TiO2. The absorption spectrum of the dye was achieved. Two kinds of dye sample were made on the basis of their places in structure of TiO2. One dye sample is solution, nanopowder of the dye in aceton. The other dye sample is film, thin film on a quartz plate. The absorption spectrums of the samples have been measured in laboratory. The measurement suggests that the dye works improves the absorption of solar energy in DSSC. This thesis mainly contains the following sections: Chapter I reviews the solar energy technology development, the research purposes, and the principles of DSSC. Chapter II introduces the theory of optical spectroscopy. Chapter III and Chapter IV describe the apparatus employed in this experimental system, the experimental method, and the testing results. Chapter V gives the conclusions drawn from the experiments.

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Six peripherally meso-modified Zn (II) porphyrin sensitizer dyes are designed and their J-V performance in dye sensitized solar cell (DSSC) evaluated. Electron-donating groups including phenothiazine, carbazole and pyrene are used to modify the porphyrin macrocycle at the meso-carbon position(s). To compare the effect of donor substitution on the performance of the cells in terms of short circuit current (Jsc), light harvesting efficiency (LHE) and power conversion efficiency (η), two sets of sensitizers with different degrees of substitution are synthesized. One set of dyes (mono-substituted) have one electron donor at trans-position to the acceptor, while the second set (tri-substituted) dyes have three of the same type electron donor groups at 5, 10 and 15 meso-carbon positions making all the six dyes push-pull type sensitizers incorporating 4'-carboxyphenyl as an electron-acceptor/anchor group. Different spectroscopic and electrochemical methods are used to study the photophysical and electrochemical properties of the dyes, while the photovoltaic performance of their cells under 1.5 A.M is studied using solar simulator. Meso-substitution of Zinc (II) porphyrin with these small donor molecules is shown to improve the light harvesting character of the Zinc (II) porphyrin macrocycle in the UV-Vis absorption while at same time improving its fluorescence quantum yield, excited-state life time and electron donating potential. All these factors combined make these meso-modified dyes better sensitizers with suitable Δ0 Δ0, and much improved power conversion efficiencies (PCE) compared to unsubstituted Zn (II) porphyrin. In particular, as a result of the peripheral modification, a doubling in efficiency in the mono- substituted series (RA-200-Zn; η=^M 4.2%, Jsc= -13.13 mA cm-2, Voc=0.54 ) and tripling in the tri-substituted series ( tri-phenothiazine Zn (II) Porphyrin; η= 7.3%, Jsc= -18.15 mA cm-2, Voc= 0.55 ) compared to unsubstituted Zn (II) porphyrin (η= 2.11%, Jsc= -5.7 mA cm-2, Voc= 0.53 V) has been accomplished.