Photonic design of embedded dielectric scatterers for dye sensitized solar cells
Embedded dielectric scatterers comprise an important approach for light trapping in dye-sensitized solar cells (DSCs) due to their simple fabrication process. The challenge in applying these scatterers lies in finding the optimal dimensions and concentration of the scatterers. This requires many experiments and it is often quite difficult to have a starting point for optimizing the concentration. Based on theories of light propagation in random media, we propose a simple model for DSCs with embedded silica spherical particles. Then, by full-wave optical calculations, we determine a narrow range for the concentration of silica particles that leads to the largest optical absorption in the cell. The simulation results were verified by realizing DSCs with different concentrations of silica particles. A power conversion efficiency of 8.08% in an 11 mu m-thick N719-sensitized DSC was achieved with 6 vol% embedded silica, which further increased to 9.30% by applying a white scattering layer on the rear-side of the counter electrode. The design approach, presented here, is a general approach that can be applied for other types of solar light harvesting structures with low optical absorption coefficient.