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

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Cu2ZnSnSe4 (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 Cu2BaxZn1‐xSnSe4 (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 MoSe2/CBZTSe back interface are observed for 50% Ba incorporation. The impact of intrinsic defects on device performance is also examined, with shallow defects like VCu and CuBa showing minimal influence at low concentrations, while deep‐level and multivalent defects such as Cui, SnCu, Sni, and Sei 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.