Low non-radiative recombination loss in CsPbI2Br perovskite solar cells

All-inorganic CsPbI2Br has attracted intensive attention due to its superior stability against thermal aging and light soaking. However, a large open circuit voltage (VOC) loss results from non-radiative recombination and the mismatched energy level alignment between CsPbI2Br and SnO2/Spiro-MeOTAD charge carrier extraction layer, has been discussed and rarely solved. Perovskite solar cells have theoretically a high value of VOC that can be obtained relative to the wide bandgap. Herein, IC61BA has been employed to modify the SnO2 surface to reduce surface defects, at the same time, a moderate energy level (CsPbI2Br)1-x(CsPbI3)x layer has been introduced at the interface between CsPbI2Br and Spiro-MeOTAD to form graded energy level alignment. As a result, correspondingly, the surface passivation and energy level tailoring reduced the energy level loss from reduced non-radiative recombination and a remarkable open circuit voltage (VOC) improved from 1.13 V to 1.34 V has been achieved, which further boosts the power conversion efficiency (PCE) of 15.56%.