Band Alignment and Defect Engineering in Barium‐Doped Cu₂ZnSnSe₄ Solar Cells: Implications for Device Performance

Abstract Cu 2 ZnSnSe 4 (CZTSe)‐based photovoltaic devices have emerged as promising next‐generation technology, with recent power conversion efficiencies surpassing 13.8%. In this study, the effects of barium (Ba) incorporation and intrinsic defects on the performance of Cu 2 Ba x Zn 1‐ x SnSe 4 (CBZTSe) photovoltaic devices are systematically explored. The interface band alignment at both the front and back contacts is analyzed by adjusting the electron affinity of CBZTSe through varying Ba content. Optimal conduction band offsets of 20 meV at the CBZTSe/CdS front interface and 40 meV at the MoSe 2 /CBZTSe back interface are observed for 50% Ba incorporation. The impact of intrinsic defects on device performance is also examined, with shallow defects like V Cu and Cu Ba showing minimal influence at low concentrations, while deep‐level and multivalent defects such as Cu i , Sn Cu , Sn i , and Se i significantly decreased efficiency due to enhanced charge carrier recombination. This study emphasizes the importance of band alignment and defect management in enhancing the performance of CBZTSe‐based PV devices and offers insights for improving their efficiency further.