Unraveling the Mechanism of Ion-Migration Suppression by Interstitial Doping for Operationally Stable CsPbI₂Br Perovskite Solar Cells

Despite the remarkable advances of inorganic perovskite solar cells (PSCs) by extrinsic metal doping, the doping mechanism and physical location of doping ions are still ambiguous. Herein, the ion-migration behavior of inorganic PSCs is studied theoretically and experimentally for Sm-doped CsPbI2Br perovskites. The structural characterizations and density functional theory (DFT) calculation confirm the interstitial occupancy of the dopant Sm in the CsPbI2Br perovskite lattice. The ion-migration behavior was systematically unveiled by employing multiple photoelectrochemical techniques. The results show that with Sm interstitial doping in the CsPbI2Br perovskite, the operational stability of PSCs is dramatically improved owing to effectively suppressed ion migration, demonstrated by alleviated VOC change at different scan rates, weaker response to electric poling, faster photocurrent response, higher activation energy of mobile ions, and much more stable maximum power point (MPP) tracking performance. With theoretical model-supported experimental investigation, this research unravels the mechanism of ion-migration suppression in CsPbI2Br PSCs by interstitial doping. This may pave the way to achieve operational stability of PSCs through facile cost-effective practice.