Omnidirectional Light Harvesting Enhancement of Cu ₂ ZnSnSe ₄ Solar Cells Decorated With Periodic ZnO Subwavelength Structures by Nanoimprint Lithography

ABSTRACT This study aims to enhance the conversion efficiency of Cu 2 ZnSnSe 4 (CZTSe) thin‐film solar cells under AM1.5G/indoor illumination by utilizing nanoimprint lithography to fabricate three types of nanostructures with periodic designs. These structures not only demonstrate efficiency improvements under both AM1.5G/indoor illumination but also exhibit good performance under high‐angle incident light and weatherability tests. Under AM1.5G illumination, the surface with/without nanostructures shows an increase in conversion efficiency from 5.54% to 9.05%, while under indoor illumination, the efficiency increases from 2.93% to 5.09%. Additionally, the surface's periodic nanostructures slightly outperform the optical enhancement of indoor light compared with that under AM1.5G illumination. In terms of weatherability testing, the efficiency decay rate of CZTSe solar cells with structures is 34.81%, significantly better than the unstructured counterpart at 48.01%. Interestingly, with increasing etching time, the characteristics of CZTSe devices not only show improvements in optical design but also exhibit self‐healing effects, enhancing interface defects and reducing carrier recombination. Thus, the improvements are not limited to optical properties but also extend to the interface layers of the device.