Titanium dioxide thin films from aqueous solution for photovoltaic applications

Titanium dioxide (titania) thin films prepared from low-temperature aqueous solution were studied for thin film photoelectrochemical (PEC) solar cells. The synthesis of titania thin film from a solution based chemical bath deposition is a promising method not only because of low cost, but also it is a low temperature process that would enable film deposition on a wide range of substrate materials, e.g. polymers. In this research, a methods for ceramic thin film processing from precursor solution has been developed to obtain thin titania films with various microstructures and thicknesses (100-2300 nm) for solar cell applications. The titania films obtained from the optimized solution process were analyzed for application to dye sensitized solar cell (DSSC) and flexible substrate PEC cells.;The photovoltaic (PV) cell performance was measured under UV light from titania films deposited on fluorine-doped tin oxide (FTO) conductive glass. Specifically, dense and porous films were produced by changing the concentration of TiCl4 and HCl in precursor solutions. Dense films were obtained at highly supersaturated solution while porous films were obtained at low supersaturation. The latter case produced aligned, dendrite-like structures, with increased surface area that exhibited a higher PV performance than those with less surface area. This aspect was also investigated by tailoring porous titania films using a polymer such as P123 tri-block copolymer or poly(acrylic acid) (PAA). Titania films with thickness up to 2.3 mum were produced with PV efficiency of about 2.31%.;Dye sensitized titania photovoltaic cells were also assembled and their PV performance under sunlight was measured. Enhanced cell efficiency was observed when adding N719 Ru dye. A cell efficiency of 0.69% was obtained from the dye applied cell as compared to 0.22% from the cell without dye applied, for which a significant difference as the current density was increased from 0.08 to 0.31 mA/cm2. In addition, TiO2 dye sensitized solar cells with PAA added showed an enhanced cell efficiency of 0.96% due to the increased surface area.;The optimized conditions of low-temperature processing have been applied to flexible PV cell fabrication. For this, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) was used as a conductive electrode for polyethylene terephthalate (PET) substrates, onto which porous TiO2 films were successfully deposited. The measured PV properties characterized by the current density, open circuit voltage, fill factor, and cell efficiency are 0.05 mA/cm2, 485mV, 0.58, and 1.18%, respectively. These values are slightly lower than those from the cells fabricated on the glass substrate partly because of the PEDOT:PSS electrode.;From this work, it was clearly shown that the PV properties with a high surface area of porous TiO2 film have a better cell performance due to increased incident light area, electrolyte contact, and dye absorption. Furthermore, TiO2 film grown thicker induces a rise of charge carrier density, which leads to high efficiency. The results obtained also suggest that the low temperature TiO2 thin films prepared from aqueous solution can be used successfully for dye sensitized photoelectrochemical solar cells and solar cells on flexible substrates.