[Abstract]

Tin (Sn²⁺) halide perovskites are promising lead-free semiconductors for optoelectronic and electronic devices, owing to their tunable bandgaps and favourable charge transport. However, their practical implementation is fundamentally limited by an intrinsic redox instability at undercoordinated Sn2+ sites, which drives uncontrolled self-p-doping and rapid oxidative degradation. Here we introduce a volatile-assisted coordination strategy that reconstructs the perovskite surface through transient acetate coordination and volatilization, which transforms reactive SnI2-terminated surfaces into chemically equilibrated and defect-mitigated interfaces. This surface reconstruction suppresses undercoordinated Sn-related trap states and stabilizes the local stoichiometry, thus enabling p-type transistors with robust transport characteristics, a near-zero threshold voltage and high on/off ratios exceeding 108. More importantly, the reconstructed interface acts as a self-passivating and thermally resilient barrier, resulting in markedly enhanced environmental stability, with devices maintaining stable operation for over 1 month at 100 °C. These results establish volatile-assisted surface reconstruction as an effective method for defect equilibration in metastable semiconductors, and they provide a general strategy for enabling durable, device-grade functionality in Sn2+-based materials.