Monolithic Two-Dimensional Photonic Crystal Reflectors for the Fabrication of Highly Efficient and Highly Transparent Dye-Sensitized Solar Cells

The transparent characteristic of dye-sensitized solar cells (DSCs) makes them suitable for building integrated photovoltaic (BIPV) devices. However, the diffusive scattering layer, which is usually used to increase the efficiency of these devices, greatly lowers the transparency of the DSC. This paper described a two-dimensional (2D) photonic crystal (PC) reflector with a sub-micrometer characteristic length that can improve the efficiency of these devices while maintaining transparency. This 2D PCs were fabricated directly onto TiO₂ photoelectrodes using colloidal lithography and have the structure of a nanopillar array. A nanopillar with a height of 430 nm was observed to selectively reflect up to 40% of the light of 400–500 nm wavelength. The perceived transparency of the 2D PC electrode was 52%, which is much higher than 0.3% of the conventional scattering layer. The DSC fabricated using the 2D PC electrode demonstrated a maximum photon-to-electric conversion efficiency of 8.23%, which is 18% higher than the pristine electrode. The 2D PC is a highly efficient and wavelength-selective reflector that can be applied to various photoelectric conversion devices.