Versatile Bidentate Chemical Passivation on a Cesium Lead Inorganic Perovskite for Efficient and Stable Photovoltaics

An all-inorganic CsPbI3 perovskite has exhibited some special excellent properties particularly high thermal stability and potential for tandem solar cells, yet its poor humidity stability and grain surface-dominated charge recombination severely hinder its applications. To overcome this dilemma, we explored a mixed-halide CsPbI2.85Br0.15 absorber layer by incorporating optimal Br ions into the CsPbI3 film (abbreviated as CsPbI3 – xBrx, x = 0.15). More importantly, versatile bidentate passivation of the CsPbI3 – xBrx perovskite is undertaken by using 2-mercaptopyridine (2-MPYD) to enhance anchoring strength, which can improve both passivation efficacy and moisture resistance simultaneously. Compared with monodentate pyridine, passivation via 2-MPYD shows better moisture resistance and longer photoluminescence lifetime. As a result, the power conversion efficiency enhanced significantly from 16.79 to 18.10% under 1 sun illumination with an open-circuit voltage (VOC) improving from 1.121 to 1.156 V, which corresponds to an Eloss decrease from 0.59 to 0.55 eV. Moreover, the CsPbI3 – xBrx film treated with 2-MPYD exhibits higher humidity stability, as it can be exposed to high ambient humidity (RH, 45–55%) for 48 h. It is logically inferred that this versatile and efficient chemical passivation method can be applied to other similar perovskite materials.