Advanced Bandgap Engineering and Interface Optimization of Zn 1‐x Mg x O Window Layers for Performance Enhancement in Sb ₂ Se ₃ Thin‐Film Solar Cells

Optimizing the window layer is a crucial strategy to enhance antimony selenide (Sb 2 Se 3 ) solar cell performance. In this work, zinc magnesium oxide (Zn 1‐x Mg x O) is proposed as a tunable wide bandgap window material to replace conventional ZnO. The Zn 1‐x Mg x O alloy provides a broader bandgap and superior thermal stability, leading to increased short‐circuit current density ( J sc ) and reduced parasitic absorption. We systematically investigated the impact of varying magnesium content (x = Mg/(Zn+Mg)) in the window layer on device performance. The broadened bandgap of Zn 1‐x Mg x O enhances the external quantum efficiency, particularly in the short‐wavelength region. Comparative simulations show that interfacing Zn 0.93 Mg 0.07 O ( E g = 3.45 eV, χ e = 4.35 eV) with CdS ( E g = 2.42 eV, χ e = 4.45 eV) produces a shallow conduction band offset (Δ E c = +0.1 eV), which reduces interfacial recombination and facilitates efficient charge extraction. Optimization indicates that x = 0.07 achieves an ideal balance of light transmission, band alignment, and device performance. The resulting Sb 2 Se 3 /CdS/Zn 0.93 Mg 0.07 O architecture reaches a simulated J sc of 36.2 mA/cm 2 and a power conversion efficiency of 11.68%, demonstrating a significant improvement over conventional ZnO‐based designs. These findings highlight the potential of Mg‐alloyed ZnO as an effective window layer for high‐performance Sb 2 Se 3 solar cells.