Unraveling the Role of Perovskite Composition on Selectivity of NiOx Hole‐Transport Layer: Correlative Analysis of Interface Chemistry and Resultant Carrier Selectivity

The performance of conventional methylammonium (MA)‐based perovskite solar cells (PSCs) and their MA‐free counterparts showcase explicit divergence in device performance often stemming from crucial open‐circuit voltage (VOC) deficits while employing NiOx hole‐transport layer (HTL). In this work, the performance of MAPbI3 and FA0.9Cs0.1PbI3 based PSCs are correlatively analyzed using surface photovoltage (SPV) and photocurrent density (Jph) studies for the first time to quantify hole selectivity and contact passivation of NiOx HTL when used in conjunction with distinct perovskite compositions. In the findings of the study, it is shown that the perovskite composition is a major determinant of NiOx HTL's carrier selectivity by regulating quasi‐Fermi level (QFL) equilibration at the absorber/HTL interface. Higher charge collection probability and SPV shown by methylammonium (MA)‐free devices highlight the suppressed formation of PbI2‐rich hole‐extraction barrier at FACsPbI3/HTL interface as opposed to MAPbI3/HTL interface, in‐turn establishing a trade‐off between carrier selectivity and contact passivation of NiOx HTL. These experimental quantifications help in understanding the evolution of internal QFL splitting and external VOC of devices employing NiOx HTL for varied perovskite composition. Therefore, to maximize the performance of PSCs, the findings of the study emphasize the significance of tailoring the energetics and kinetics at the perovskite/HTL interfaces.