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 CsPbIBr2 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 SnO2 electron transport layer (ETL) and the CsPbIBr2 photoabsorber to passivate the undesirable recombination, thereby enhancing the V-oc. Meanwhile, the delta-phase perovskite located at the interface between SnO2 ETL and CsPbIBr2 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 CsPbIBr2 PSCs to obtain a PCE of 11.04%, which is the highest value among the pure-CsPbIBr2 PSCs. However, the MgO layer significantly reduces severe hysteresis and increases device stability.