In-Vacuum Electron-Beam-Evaporated MgF₂/MgO Bilayer on TiO₂ Boosts Efficiency and Stability in All-Inorganic...

Interface losses at the buried electron-transport-layer (ETL) side remain a key bottleneck for high-performance all-inorganic perovskite solar cells, largely arising from poor precursor wetting, uncontrolled crystallization, and defect-assisted nonradiative recombination. Here we report a solvent-free, vacuum-compatible approach by in-vacuum deposition of an ultrathin MgF₂/MgO bilayer on TiO₂ via electron-beam evaporation. The MgF₂ sublayer improves surface wettability and precursor spreading, thereby lowering the nucleation barrier and regulating crystallization kinetics to form compact perovskite films with enlarged grains and suppressed interfacial voids. The MgO overlayer further reduces oxygen-vacancy-related defect states at the TiO₂ 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.