Solution‐Processed Magnesium Oxide Buffer Layer for Improved Stability of CsPbI ₂ Br Perovskite Solar Cells

The application of inorganic Cs‐based perovskites in solar cells (PSCs) has gained increasing attention as a viable alternative to hybrid organic–inorganic counterparts. However, their device performance and stability remain limited by interfacial and intrinsic material instabilities. To address these challenges, a solution‐processed MgO layer is employed for interfacial engineering at the ZnO/CsPbI 2 Br interface. Incorporating MgO onto the ZnO electron transport layer (ETL) leads to significant improvements, including enlarged perovskite grain size, reduced trap density, and enhanced electron mobility. Moreover, the incorporation of MgO increases the conduction‐band energy offset at the ETL/perovskite junction, resulting in a consistently higher open‐circuit voltage of PSCs. Stability assessments show that MgO‐incorporated devices exhibit significantly improved shelf lifetime. The MgO‐incorporated PSC, without encapsulation, stabilizes at an efficiency of 15.3% during a 10 000 s current–time test under maximum power point bias, compared to 10.4% for the control device. Furthermore, proton‐irradiation tests simulating the low Earth orbit conditions demonstrate that MgO‐incorporated devices retain their initial efficiency after 11 weeks, whereas control devices decline to 47% of their initial value. Overall, this work highlights the crucial role of MgO in interfacial engineering for inorganic Cs‐based PSCs and provides valuable insights for the development of cost‐effective, radiation‐tolerant, and stable photovoltaic devices.