Full-Spectrum Absorption Enhancement in a-Si:H Thin-Film Solar Cell with a Composite Light-Trapping Structure

Thin-film solar cells are favorable because of the reduced material and fabrication cost as well as the advantage of mechanical flexibility. However, due to the reduced thickness of the active layer, the light absorption is also decreased. Herein, a composite light-trapping structure with a double-layer antireflection coating on the upper surface and Ag hemispheres on the substrate is proposed to achieve full-spectrum (350-800 nm) absorption enhancement. The results simulated by the finite-difference-time-domain method show that compared with 100-nm-thick bare a-Si:H solar cell, the short-circuit current density (J(sc)) and photoelectric conversion efficiency are respectively improved by 39% and 38% through adding the optimized composite light-trapping structure. Excitingly, the light-trapping effects remain efficient over different thicknesses of the active layer, and the J(sc) of a 400-nm-thick a-Si:H thin-film solar cell can be enhanced to approach the theoretical limit. The light-trapping method proposed in this study can provide general and valuable guidance for improving the light absorption in various thin-film solar cells.