Hierarchically structured photoelectrodes for dye-sensitized solar cells

This paper highlights several significant achievements in dye-sensitized solar cells using hierarchically structured photoelectrodes that consist of spherical or one-dimensional assemblies of ZnO or TiO2 nanocrystallites. It shows that, besides providing a large surface area for dye adsorption, more importantly, the hierarchically structured photoelectrodes may improve the solar cell’s performance by imparting extra functions, such as (1) generating light scattering owing to the size of assemblies being comparable to the wavelengths of the incident light, (2) enhancing electron transport due to the compact packing of the nanocrystallites that form the assemblies, and (3) facilitating electrolyte diffusion as a result of the relatively open structure of the photoelectrode films composed of spherical or one-dimensional assemblies.