Numerical Optimization of Wurtzite and Kesterite‐Based Heterojunction Thin‐Film Solar Cells Using SCAPS‐1D

ABSTRACT The development of earth‐abundant and non‐toxic absorber materials is essential for the sustainable advancement of thin‐film photovoltaics. In this work, we numerically investigate heterojunction thin‐film solar cells based on wurtzite ZnSnN 2 and kesterite Cu 2 ZnSnS 4 (CZTS) using the SCAPS‐1D simulator. A device structure of FTO/ZnSnN 2 /CZTS/Au was modeled, and the impact of key parameters such as absorber thickness, carrier concentration, defect density, and interface properties on device performance was systematically optimized. The results reveal that ZnSnN 2 , with its suitable wide bandgap, serves as an efficient window/absorber layer complementing the narrow‐bandgap CZTS, thereby enhancing photon absorption across the solar spectrum. After optimization, the heterojunction device achieves a maximum power conversion efficiency of 27.09%, with an open‐circuit voltage of 1.12 V, short‐circuit current density of 29 mA cm −2 , and a fill factor of 83.32%. These findings highlight the promising potential of ZnSnN 2 /CZTS heterojunctions as a cost‐effective and environmentally benign route toward high‐performance thin‐film solar cells.