Multi-functional photoanode films using mesoporous TiO2 aggregate structure for efficient dye sensitized solar cells

We present here the photovoltaic performance of dye sensitized solar cells (DSCs) using sub-micron sized mesoporous TiO2 aggregates which incorporate built-in multi-functional properties such as high dye uptake, efficient light scattering and enhanced charge collection. The DSC prepared with these mesoporous anatase TiO2 aggregates as photoanode with no additional scattering layer exhibits an enhanced conversion efficiency of 9.00% at 1 sun and 10.84% at 0.16 sun illumination. The properties of the photoanode film in DSCs were analyzed by surface area, diffuse reflectance, intensity modulated photocurrent/voltage spectroscopy (IMPS/IMVS) and electrochemical impedance spectroscopy (EIS) measurements in order to gain knowledge of the decisive factors contributing to such high power conversion efficiency. The present study reveals that the mesoporous aggregate offers large internal surface area and high light scattering with its unique structure. Due to the high crystallinity and compact packing of primary nanocrystallites forming the aggregate structure of mesoporous TiO2, the electron diffusion length is substantially long reflecting a lower number of electrons trapped at the grain boundaries. A good compromise of electron transport time and extended life time in mesoporous aggregate films compared to their non-aggregate counterparts leads to efficient charge collection and higher power conversion efficiency.