Ag‐Induced Phase and Defect Engineering of Co‐Evaporated <scp> Sb ₂ Se ₃ </scp> Thin Films for Enhanced Photovoltaic Performance

High‐efficiency antimony selenide (Sb 2 Se 3 ) solar cells remain limited by anisotropic charge transport, high defect density, and rapid back‐contact recombination. We demonstrate a simple co‐evaporation strategy for introducing an ultrathin Ag interlayer at the Sb 2 Se 3 /Mo interface. The proposed strategy significantly enhances the performance of the fabricated devices. Incorporation of an Ag layer promotes grain growth, improves crystallinity, and passivates bulk defects, thereby suppressing interfacial recombination and enhancing both the open‐circuit voltage and fill factor. Structural analyses reveal an orientation transition of the quasi‐one‐dimensional orthorhombic Sb 2 Se 3 ribbons from a preferred (hk1) orientation to a random one. This transition is driven by the sequential reaction of Ag with Se to form Ag 2 Se, which subsequently reacts with Sb 2 Se 3 to yield AgSbSe 2 . However, when the Ag content exceeds the optimal level, unreacted Ag 2 Se accumulates at the bottom of the film, degrading device performance. Time‐resolved photoluminescence and capacitance measurements confirm reduced defect densities and optimized junction properties. The optimized Sb 2 Se 3 device incorporating the Ag interlayer achieves a power conversion efficiency of 5.56%, outperforming the Ag‐free counterpart under standard AM 1.5G illumination. The proposed strategy offers a promising route to high‐performance Sb 2 Se 3 thin‐film photovoltaics and provides a pathway for tandem integration of Sb 2 Se 3 ‐based devices.