Charge transfer investigations of solid state dye sensitized solar cells by ordered TiO2 nanostructures as photoanode

PV technologies are an alternative to today's energy needs. In this context, sDSSCs, which are among the third generation solar cells, are being studied intensively due to their low cost, easy production, and stability. Within the scope of this doctoral study, improvement of the charge transfer mechanism on the photo-anode has been studied to increase the performance of sDSSC. For this purpose, the nanocrystal TiO2 material with mesoporous structure and the TiO2 nanowires with one-dimensional crystal structure were used for sDSSC fabrication and their optical, structural, morphological and electrical characterizations were investigated. In order to analyze the performance of solar cells, it is vital to understand the processes such as charge transfer and recombination between the interfaces. Impedance spectroscopy is an essential and powerful tool in order to clarify the internal dynamics of sDSSC. The charge transfer and transport dynamics such as electron lifetime, diffusion coefficient and diffusion length are determined by EIS measurements. IMPS illuminates the charge transport dynamics, whereas IMVS measurements provide information on electron recombination lifetime and charge recombination dynamics. Thus impedance spectroscopy provides valuable information about the optimizations of charge transfer dynamics and the rate of recombination that determines the efficiency of a solar cell. In the thesis study, in Section 3.1, the sDSSCs, fabricated with TiO2 nanocrystals, were optimized by current-voltage and impedance spectroscopy and the charge dynamics of the efficient devices were investigated. The sDSSC performance parameters were explained by the obtained results. In section 3.2, the structural, optical and electronic properties of TiO2 nanowires, synthesized in different time periods by hydrothermal method, were investigated. Firstly, the synthesis time of the TiO2 nanowires was obtained for the highest efficiency of sDSSC. Then TiO2 nanowires were branched with TiCl4 at different incubation times and TiO2 / dye interface area was optimized. In this way, both high-rate photo-electron production and HTM material penetration between TiO2 nanowires are aimed by the optimal branching incubation time. Thus, the electron regeneration of the HTM material to the dye is achieved efficiently, and the photo-current is transmitted through the nanowires with a low recombination rate. In section 4, the advantages and disadvantages of two different structure of TiO2 were clarified by comparing the obtained results of sDSSCs.