Plasmonic modulated back reflector for thin film photovoltaics

Abstract

Light trapping is an essential aspect in the design of photovoltaics based on thin absorbers. Incorporation of textured surface with different nanostructures is the main strategy for light trapping in all kinds of thin film photovoltaic (TFPV) cells. Highly textured back reflector (BR) with a composite structure of Al/Ag/ZnO proposed in this article could improve light-trapping performance of TFPVs, but studies on optical absorption revealed that at the Al/Ag interface existed parasitic surface plasmon polaritons (SPPs). A plasmonic modulated BR (PMBR) with a dielectric layer introduced at the Al/Ag interface was deeply analyzed in this study. It could effectively ameliorate the parasitic absorption in the 300–500 nm wavelength range while maintaining the light-trapping effect. When it was applied in a surface enhanced Raman scattering (SERS) structure, results showed that a thin dielectric layer, as 20 nm undoped ZnO used here, could effectively prevent the local electromagnetic field evanescing at the Al/Ag interface. Using the optimized PMBR structure, active-area conversion efficiencies of 8.55%, 8.83% and 12.6% for a normal nc-Si:H single-junction cell, an ultra-thin a-Si:H single-junction cell and an a-Si:H/a-SiGe:H/nc-Si:H triple-junction cell were achieved, respectively. These findings could also be applied to other solar cells including silicon heterojunction, copper indium gallium selenide (CIGS), perovskite or tandem solar cells in which light management and modifications also need to be considered.