Light scattering enhancement from sub-micrometer cavities in the photoanode for dye-sensitized solar cells
A simple cell architecture that achieves enhanced light harvesting with less dye quantity while simultaneously improving the power conversion efficiency (PCE) of dye-sensitized solar cells is presented. Polystyrene (PS) spheres of sub-micrometer size were incorporated into the titanium dioxide paste resulting in photoanodes with bimodal pore size distribution. Scanning electron micrographs of TiO2 films revealed a mixture of mesoporous and macroporous morphology in which sub-micrometer cavities created by the combustion of PS increased the light scattering, enhancing the optical path length and hence the harvesting of photons by the sensitizer. The amount of dye uptake by these films is lower than that of standard films because the high porosity reduces the total surface area. Even with lower dye adsorption, the photovoltaic performance has been maintained and even improved, mainly due to better open circuit voltage and higher fill factor. Overall, better light harvesting has helped to maintain the efficiency of dye-sensitized solar cells while saving up to 30% of dye loading and replacing the conventional 400 nm scattering layer with voids. By employing these photoanodes, an efficiency of 6.9% was achieved in ionic liquid based dye sensitized solar cells.