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 ( V OC ) deficits while employing NiO x hole‐transport layer (HTL). In this work, the performance of MAPbI 3 and FA 0.9 Cs 0.1 PbI 3 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 PbI 2 ‐rich hole‐extraction barrier at FACsPbI 3 /HTL interface as opposed to MAPbI 3 /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.