Unraveling the Role of Perovskite Composition on Selectivity of NiO_x 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 (V_OC) deficits while employing NiO_x hole‐transport layer (HTL). In this work, the performance of MAPbI₃ and FA_0.9Cs_0.1PbI₃ based PSCs are correlatively analyzed using surface photovoltage (SPV) and photocurrent density (J_ph) studies for the first time to quantify hole selectivity and contact passivation of NiO_x 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 NiO_x 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 NiO_x HTL. These experimental quantifications help in understanding the evolution of internal QFL splitting and external V_OC of devices employing NiO_x 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.