Light scattering with oxide nanocrystallite aggregates for dye-sensitized solar cell application

Oxide nanocrystallite aggregates are candidates for use in dye-sensitized solar cells. The aggregates are of submicron size, formed by nano-sized crystallites and, therefore, able to offer both a large specific surface area and desirable size comparable to the wavelength of light. While used for a photoelectrode in a dye-sensitized solar cell, the aggregates can be designed to generate effective light scattering and thus extend the traveling distance of light within the photoelectrode film. This would result in an enhancement in the light harvesting efficiency of the photoelectrode and thus an improvement in the power conversion efficiency of the cell. When this notion was applied to dye-sensitized ZnO solar cells, a more than 120% increase in the conversion efficiency was observed with photoelectrode film consisting of ZnO aggregates compared with that comprised of nanocrystallites only. In the case of TiO2, the photoelectrode film that was formed by TiO2 aggregates presented conversion efficiency much lower than that obtained for nanocrystalline film. This may be attributed to the non-ideal porosity of the TiO2 aggregates and the unsuitable facets of the nanocrystallites that form to the aggregates. However, a 21% improvement in the conversion efficiency was still observed for the TiO2 films including nanocrystallites mixed with 50% aggregates, indicating the effectiveness of the TiO2 aggregates as light scatterers in dye-sensitized solar cells. Optimization of the structure and the surface chemistry of TiO2 aggregates, aiming to yield more significant improvement in the conversion efficiency of dye-sensitized solar cells, is necessary.