Rapid Low‐Temperature In‐Situ Liquid Epitaxy Toward Oriented Perovskite Heterojunctions for High‐Performance X‐Ray Detection

Severe ion migration in conventional metal halide perovskites (MHPs) induces dark current drift and photocurrent degradation, severely restricting their commercialization in X‐ray detection. Herein, we propose a low‐temperature and rapid in‐situ liquid‐epitaxial strategy to grow highly crystalline MAPbI 3 /MAPbBr 3 /MAPbI 3 sandwich heterojunctions, where precursors dissolved in 2‐methoxyethanol (2‐Me) favor fast mass transfer. Achieved MAPbI 3 /MAPbBr 3 /MAPbI 3 heterojunctions with a type‐I band alignment facilitate efficient carrier separation and transport, as well as suppression of traps. By changing epitaxial growth time, MAPbI 3 layers with variable thicknesses are uniformly deposited on bulk MAPbBr 3 , enabling an optimal trade‐off between X‐ray absorption and carrier transport. Benefiting from high bulk resistivity and minimized trap density, the heterojunction X‐ray detectors achieve a high sensitivity of 38301 µC Gy −1 cm −2 and a low limit of detection of 390 nGy s −1 , markedly superior to intrinsic MHP counterparts. More importantly, the built‐in interfacial electric field significantly mitigates halide ion migration, endowing the device with exceptional long‐term operational stability and high‐resolution X‐ray imaging capability. This work provides a feasible preparation of high‐quality MHP heterojunction for the development of high‐performance and stable X‐ray detectors.