Broadband absorption enhancement using front pre-patterned substrate for thin film amorphous silicon solar cell

Light trapping in amorphous silicon thin film solar cells has been an intensive study owing to the low absorption coefficient in near-infrared. We demonstrate a frontal pre-patterned substrate (PPS) on amorphous silicon solar cells, utilizing scalable colloidal lithography, to serve both functions of anti-reflection and light trapping effect. We show that a solar cell with front pre-patterned substrate exhibits broadband enhanced external quantum efficiency due to both anti-reflection and light-trapping, with respect to an industrial standard cell using an Asahi U glass substrate which is mostly optimized for light trapping. The power conversion efficiency of the pre-patterned cell is measured 8.38%, which shows 56.34% and 8.83% enhancement compared to the reference cell with a flat substrate and the commercialized Asahi U-type substrate, respectively. Moreover, the angle-resolved absorption spectroscopy shows superior optical coupling to the absorber layer at large angles of incidence (AOIs), which guarantees sufficient light harvesting for the entire day. We also present a design optimization of frontal pre-patterned substrate with broadband antireflective subwavelength structures based on the theoretical calculation using a rigorous coupled wave analysis (RCWA) method. We can find the optimization size of PPS is 500nm bottom width and 450nm height from the simulation enhancement mapping figure.