Design of Multilayers of Urchin-like ZnO Nanowires Coated with TiO₂Nanostructures for Dye-Sensitized Solar Cells

In dye-sensitized solar cells, the photovoltaic efficiency of nanowires (NW) is still limited by their surface area and loss of light absorption compared with nanoparticle (NP) architectures. To overcome this limitation, the light harvesting efficiencies must be improved by increasing the total NW array surface area, without increasing too much the traveled distance of electrons. Here, we describe the design of a 3D architecture based on polystyrene spheres (PS) coated with ordered multilayers of urchin-like ZnO NWs (U-ZnO NWs) to be used as a high surface area nanostructure photoanode for dye-sensitized solar cells. Two to four layers of U-ZnO NWs were synthesized by using PS of 1 and 5 μm in diameter. The ordered layers of U-ZnO NWs were then coated with a thin layer of TiO2 by atomic layer deposition, and topped with a ∼9–14 μm thick layer of anatase TiO2 NPs. We found that assembling organized layers of U-ZnO NWs significantly increased the surface area and provided better photon absorption. Moreover, coating the U-ZnO NWs with a thin TiO2 layer decreased the charge recombination and consequently enhanced the photovoltaic efficiency.