Tin Substitution Stabilizes 2D Perovskite Epitaxial Heterostructures for High‐Mobility, Hysteresis‐Free Field‐Effect Transistors

Abstract Halide ion migration in 2D perovskite heterostructures has long hindered the realization of their extraordinary optoelectronic properties, resulting in current–voltage hysteresis and reduced device stability. Here, it demonstrated that tin (Sn) substitution at the perovskite B‐site effectively stabilizes ultrathin 2D halide perovskite epitaxial heterostructures by suppressing halide ion migration and boosting charge transport. Density functional theory (DFT) calculations indicate that Sn 2+ incorporation raises the energy barrier for halide migration, optimizes band alignment, and lowers the effective hole mass, collectively mitigating ionic instability and promoting efficient interfacial charge transfer. As a result, field‐effect transistors (FETs) based on (PEA) 2 Pb 0.7 Sn 0.3 Br 4 ‐(PEA) 2 PbI 4 (PEA = phenylethylamine) heterojunctions achieve hysteresis‐free operation, a subthreshold swing of 813 mV dec −1 , an on/off ratio of 2.52 × 10 6 and a hole mobility of 8.41 cm 2 V −1 s −1 , positioning them among the high‐mobility p‐type 2D perovskite thin‐film FETs reported to date. These findings advance a robust strategy for stabilizing 2D perovskite heterostructures and open new pathways for integrating them into next‐generation electronic and photonic systems.