Halogenated Ethylamine Hydrochloride Modulation Facilitating a V_OC of 1.19 V in Perovskite Solar Cells

Abstract Interface engineering has emerged as an effective strategy for optimizing the charge carrier dynamics in perovskite solar cells, and the design of modulators plays a crucial role in improving interface effects. Here, halogenated ethylamine hydrochloride (XEA), such as 2‐fluoroethylamine hydrochloride (FEA), 2‐chloroethylamine hydrochloride (CEA), or ethylamine hydrochloride (EA), is incorporated into the buried interface between perovskite layer (PVK) and SnO₂ electron transport layer (ETL) to assist crystal growth, tune the energy level and passivate defects. Pre‐embedded XEA interacts with PbI₂ to form a 2D mesophase. The mesophase assists the growth dynamics and orientation of the epitaxial perovskite, resulting in uniform perovskite films with larger grains and higher densification, effectively reducing the defects caused by excess PbI₂ at the buried interface. NH₃⁺ cation and X⁻ anion ions on XEA fill and coordinate the vacancies, passivating the defects in SnO₂ and perovskite. Meanwhile, the introduction of XEA adjusts the energy match between PVK/ETL, compensating the energy loss at the buried interface. Consequently, the FEA‐modified devices exhibited a power conversion efficiency of 24.7%, featuring an exceptionally high open‐circuit voltage of 1.19 V and remarkable stability.