Boosting spectral response at band edge and charge transport in CZTSSe solar cells by periodic Mo back-contact texturing

This study utilizes magnetron sputtering combined with a metal mask attached to the Mo surface to fabricate a periodic protruding array microstructure. By optimizing the mask specifications (200-mesh optimal) and sputtering time (100-s optimal), the Mo surface was textured. Experimental results demonstrate that this periodic microstructure effectively modulates the spatial distribution of reflected angles for incident sunlight (primarily near-infrared band edge light with deep penetration depth) reaching the Mo back contact in Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. This significantly extends the effective optical path length, thereby enhancing photon absorption utilization. Concurrently, the periodic structure improves the crystallinity of the absorber layer, optimizes carrier transport properties, and effectively suppresses the concentration of interfacial and bulk defects. Benefiting from these synergistic improvements in both electrical and optical performance, the power conversion efficiency of the CZTSSe devices increased from 11.59% to 12.82%. The entirely physical optimization scheme employed here offers high controllability and excellent compatibility with other process enhancements, presenting a straightforward and effective strategy for improving absorber crystal growth and light management in photovoltaic devices.