TiO₂ hierarchical sub-wavelength microspheres for high efficiency dye-sensitized solar cells

Monodisperse anatase hierarchical microspheres were produced via a simple sol-gel process. These microspheres in the sub-wavelength diameter of 320-750 nm could scatter visible light efficiently as whispering gallery modes (WGM) corresponding to the dye sensitized wavelength, and load a large number of dye molecules with a large surface area (149.82 m² g^-1). Dye-sensitized solar cells (DSCs) based on the microsphere monolayer adsorbed light fully over the entire wavelength region and facilitated electrolyte diffusion due to larger voids between the microspheres, compared to the conventional film. Furthermore, the dynamics of electron transport and recombination was investigated systematically, indicating the higher charge collection efficiency of the TiO₂ microsphere film. Overall, DSCs based on the 7.5 μm hierarchical microsphere monolayer exhibited more outstanding photovoltaic performances, yielding a high power conversion efficiency (PCE) of 11.43% under simulated AM 1.5 sunlight. Half of the normal film thickness was used to cut the device cost significantly.