Interface Modulator of Ultrathin Magnesium Oxide for Low‐Temperature‐Processed Inorganic CsPbIBr2 Perovskite Solar Cells with Efficiency Over 11%

Although the power conversion efficiency (PCE) of thermally stable inorganic CsPbIBr 2 perovskite solar cells (PSCs) is over 10%, the severe interfacial and nonradiative recombination deteriorates the open‐circuit voltage ( V oc ). Herein, an ultrathin wideband MgO is mediated between the SnO 2 electron transport layer (ETL) and the CsPbIBr 2 photoabsorber to passivate the undesirable recombination, thereby enhancing the V oc . Meanwhile, the δ‐phase perovskite located at the interface between SnO 2 ETL and CsPbIBr 2 film is reduced after MgO modification, because the MgO layer provides a substrate for perovskite growth and reduces vacancy. Moreover, the tunneling effect and better band alignment effectively block holes and accelerate electrons to the electrode. Consequently, for optimal MgO‐modified devices, a shining improvement of V oc from 1.25 to 1.36 V without short‐circuit current losses boosts the champion CsPbIBr 2 PSCs to obtain a PCE of 11.04%, which is the highest value among the pure‐CsPbIBr 2 PSCs. However, the MgO layer significantly reduces severe hysteresis and increases device stability.