Ionic Dipolar Switching Hinders Charge Collection in Perovskite Solar Cells with Normal and Inverted Hysteresis

Abstract

Drift-diffusion modeling of the ionic dipole switching from the measurement of fast scanned and long pre-biased electrical response is proposed as a novel protocol for evaluation of limit hysteretic effects in perovskite solar cells. Up to eight systems were measured including CH3NH3PbI3, Cs0.1FA0.74MA0.13PbI2.48Br0.39 and FA0.83MA0.17Pb1.1Br0.22I2.98 3D perovskite absorbers, as well as 2D capping layers towards the selective contacts. We show systematic hysteretic patterns, even among typical hysteresis-free devices, including normal and inverted hysteresis as general dissimilar trend between CH3NH3PbI3 and mixed perovskite cells, respectively. Particularly, strong changes in the short-circuit current density ( Jsc ) were identified, in addition to different trends affecting the fill factor (FF) and the open-circuit voltage (Voc ). The changes in Jsc were analyzed with state-of-the-art numerical drift-diffusion simulations concluding in an important reduction in the charge collection due to ionic distribution switching depending on the pre-biasing protocol and the type of absorbing perovskite. It is shown that mixed perovskites inhibit ionic dipolar switching. In addition, our calculi signal on the required conditions for the occurrence of inverted hysteresis and changes in the Voc . Regarding the FF and Voc patterns a new empirical approach is introduced and corresponding interpretations are proposed.