An Impressive Open‐Circuit Voltage of 1.223 V and High Humidity Stability of Perovskite Solar Cells with MgO Buffer Layer Deposited by Low‐Temperature Atomic Layer Deposition

Abstract The performance of perovskite solar cells has been continuously improving. However, humidity stability has become a key problem that hinders its promotion in the process of commercialization. A buffer layer deposited by atomic layer deposition is a very helpful method to solve this problem. In this work, MgO film is deposited between Spiro‐OMeTAD and electrode by low‐temperature atomic layer deposition at 80 °C, which resists the erosion of water vapor, inhibits the migration of electrode metal ions and the decomposition products of perovskite, then finally improves the stability of the device. At the same time, the MgO buffer layer can passivate the defects of porous Spiro, thus enhancing carrier transport efficiency and device performance. The Cs 0.05 (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 perovskite device with a MgO buffer layer has displayed PCE of 22.74%, also with a high V oc of 1.223 V which is an excellent performance in devices with same perovskite component. Moreover, the device with a MgO buffer layer can maintain 80% of the initial efficiency after 7200 h of storage at 35% relative humidity under room temperature. This is a major achievement for humidity stability in the world, providing more ideas for further improving the stability of perovskite devices.