Self‐Passivating Perovskite‐Electrode Interfaces Enabled by Field‐Induced Phase Transformation

Halide perovskites are promising semiconductors for optoelectronic and radiation‐detection applications, yet their operational stability is often constrained by dynamically uncontrolled electrode/perovskite interfaces under electrical bias. Here, we report a self‐passivating perovskite–electrode interface enabled by field‐induced phase transformation. Unlike conventional molecular passivation or buffer‐layer engineering, this strategy exploits chemical potential differences among the metal electrode, halide species, and ambient environment to redirect bias‐driven interfacial reactions into adaptive stabilization. Using Bi/FAPbBr 3 as a model system, we show electrical bias drives a controllable in situ electrochemical transformation that converts the contact into dense, and self‐limiting BiOBr interlayer while preserving the perovskite bulk. This metal oxyhalide layer provides robust interfacial bonding, favorable energy‐level alignment, and ultradense nanometer‐scale barrier against further ionic accumulation and degradation. As a stringent demonstration under kilovolt‐level bias, γ‐ray detectors based on this adaptive junction tolerate up to 1000 V and achieve an energy resolution of 3.6 keV at 122 keV, among the best values reported for perovskite γ‐ray detectors. This work establishes field‐induced interfacial phase transformation as a general strategy for stabilizing perovskite contacts under realistic operating conditions.