SiO2/ZnSe anti-reflection coating for solar cells

This paper reports a proposal and demonstration of a novel anti-reflection coating (ARC) using a dielectric material, such as SiO₂, in conjunction with lattice-matched and conductive crystalline ZnSe for GaAs based solar cells. The application of such an ARC to GaAs single-junction solar cell is used for the feasibility study. The transfer matrix method is applied to calculate the reflectance as well as determine the optimal SiO₂ and ZnSe layer thicknesses. The simulation results indicate that a minimum reflection loss of 1.5% is achievable when the SiO₂ and ZnSe layer thicknesses are 91 nm and 49 nm, respectively. Test structures consisting of ZnSe and SiO2 layers were grown using molecular beam epitaxy and magnetron RF sputtering, respectively. The reflectance measurements of both samples showed 4.0% total reflection loss over the absorbed solar spectrum. This newly proposed ARC can also be used for multi-junction solar cells based on GaAs as well as other single- or multi-junction solar cells based on different substrates. The single-crystal ZnSe layer with proper doping can also be used for current spreading to further improve the overall solar cell efficiencies.