Manipulation of Ion Migration in Inverted Perovskite Solar Cell with Rubidium-Doped NiO _<i>x</i> Hole Transport Layer

Ion migration is considered a dominant factor responsible for the poor stability of perovskite solar cells (PSCs). Alkali metal doping into the hole transport layer (HTL) has emerged as an effective strategy for regulating ion migration, yet the detailed landscape in PSC devices is still poorly clarified. Here, we systematically investigate the influence of Rb+ doping in NiOx HTLs on ion migration in inverted PSCs using a custom-built circuit-switched transient photoelectric technique (cs-TPT). By decoupling the electronic and ionic contributions to photovoltage output, we provide direct evidence that ion migration can be effectively suppressed with increasing Rb+ concentration. Combining the well-established band alignment regulation of Rb+ doping and the model of polarization-induced trap states, we attribute this suppression to a reduced driving force for ion accumulation at the perovskite/HTL interface. More importantly, the suppressed ion migration occurs independently of the photovoltaic performance, which remains largely unchanged across all tested devices, providing a mechanistic framework for understanding ion migration in inverted PSCs.