In-Vacuum Electron-Beam-Evaporated MgF ₂ /MgO Bilayer on TiO ₂ Boosts Efficiency and Stability in All-Inorganic Perovskite Solar Cells

surface and decreases interfacial trap density, as supported by the attenuated defect components in XPS and the reduced trap density extracted from space-charge-limited-current measurements. With the improved buried-interface quality, nonradiative recombination is effectively suppressed, and charge extraction/transport is accelerated, leading to reduced hysteresis and enhanced photovoltaic performance. As a result, the open-circuit voltage increases from 1.031 to 1.126 V, and the power conversion efficiency improves from 14.71 to 18.22%. Moreover, the dense inorganic bilayer enhances moisture tolerance and operational stability of unencapsulated devices. This in-vacuum, evaporation-based buried-interface engineering provides a scalable route toward efficient and stable all-inorganic perovskite photovoltaics.