Mesoporous Perovskite Solar Cells And Novel Oxide Solar Cells

As opposed to conventional resources such as coal and fossil fuels, solar energy is considered as reliable, inexhaustible and clean energy source. Photovoltaic is one of potential approaches that converts solar energy into electricity, and can serve as a mean to solving the disturbing issues of global energy crisis and environmental pollution that humanity being are facing now.Organic-inorganic halide lead perovskite (CH3NH3PbX3, X=Cl, Br, I) materials have shown great promise in thin-film photovoltaic devices owing to their excellent light absorption coefficient, long diffusion length, the appropriate band gap, and the ease to fabricate these materials with solution process. Recently, the power conversion efficiency (PCE) of the mesoporous perovskite solar cells have skyrocketed form3.8%to more than20%in just5yearsIn this dissertation, morphology and photovoltaic performance depending on deposition procedures of CH3NH3bI3have been studied. CH3NH3bI3perovskite light absorber is deposited on the mesoporous TiO2layer via one-step and two-step coating methods and their photovoltaic performances are compared. We employed impedance spectroscopy (IS) to investigate the factors responsible for the different voltages of the perovskite solar cells based on one-step and two-step process. The result shows that recombination kinetics was significantly affected by the different morphology of the perovskite.Secondly, mesoporous TiO2nanoparticle film is usually used as electron-transporting materials (ETMs) and scaffold layer for high-efficiency perovskite solar cells. Despite the remarkable achievement in pervoskite solar cells, development of alternative ETMs/scaffold to TiO2is a promising avenue to further improve the performance of perovskite solar cells. In this dissertation, we present solid-state perovskite solar cells utilizing mesoporous SnO2electrodes as a HTM and and scaffold layer, CH3NH3bI3as a light-absorber and spiro-OMeTAD as a HTM. By optimizing the thickness of the SnO2film and treating the surface of the SnO2nanoparticles with TiO2aqueous solution, the short-circuit current density and open-circuit voltage have been increased to nearly18mA/cm2and1V, respectively, resulting in devices with over10%PCE. Impedance spectroscopy results indicated that the ultrathin TiO2coating on the SnO2film as a result of TiO2treatment significantly retards the charge recombination process between HTM, perovskite and SnO2film.Furthrmore, colloidal PbS QDs prepared by a hot injecting method has been successfully introduced in the mesoporous perovskite solar cells as inorganic hole-transporting materials, and to replace the expensive HTM, e.g. spiro-OMeTAD. Compact crystalline morphology of the CH3NH3PbI3capping layer significantly retarded the recombination process between electrons in TiO2and HTMs. These results indicate the efficiency of PbS QDs as a low cost HTM and point out the importance of retarding recombination in a perovskite/QD hybrid solar cell.Perovskite materials are highly sensitive to water (moisture). The decomposition of perovskite in the presence of water is very fast. Recently, a new field in photovoltaics has emerged, focusing on solar cells that are entirely based on metal oxide semiconductors. In this dissertation, a robust, environmentally friendly and visible-light-responsive oxide semiconductor BiVO4have been firstly synthesized by employing facile successive ionic layer adsorption and reaction (SILAR) deposition technique and used as a sensitizer for oxide solar cells using porous TiO2and SnO2films, respectively. The optical properties and microstructures of BiV4/TiO2heterjunction were analyzed by UV-vis, XRD, and TEM. It is found that BiVO4can be used as an effective sensitizer in the mesoporous sensitized solar cells. Those results not only demonstrate a simple method to prepare BiVO4quantum dots based solar cell, but also provides important insights into the low bandgap oxide solid-state sensitized solar cells.