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 (V-OC) 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 V-OC that can be obtained relative to the wide bandgap. Herein, IC(61)BA 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 (V-OC) improved from 1.13 V to 1.34 V has been achieved, which further boosts the power conversion efficiency (PCE) of 15.56%.