Structural, optical and photoelectrochemical studies on the nanodispersed titania

Nanodispersion of aggregated TiO₂ powders has been performed by microbead milling and its effect on photovoltaic performance has been investigated with dye-sensitized solar cell. Plasma-treated 30 μm-diameter zirconia beads are used to disperse the aggregated nanocrystalline TiO₂ powders in ethanolic medium. Particle size distribution, surface area, film morphology, porosity, transmittance and haze are investigated with different milling speed. Microbead milling leads to a reduction of particle size, narrow size distribution and increase of surface area. A slight crystal phase transformation from anatase to rutile is also observed after microbead milling. Optical property is found to be influenced by microbead milling speed, where transmittance increases and haze decreases with increasing milling speed. Compared with photovoltaic performance of dye-sensitized solar cells based on titania before and after microbead milling, overall conversion efficiency is substantially improved from 4.46% to 6.31% after microbead milling at 2490 rpm for 90 min, corresponding to 42% increment, which is mainly due to a noticeable increase in photocurrent density, associated with highly dispersed characteristics. According to the photocurrent and photovoltage transient spectroscopic study, time constant for electron transport is hardly affected, while that for recombination is slightly decreased due to the increased surface area by nanodispersion.