Highly Stable and Sensitive (PEA)₂PbBr₄/CsPbBr₃ Single‐Crystal Heterojunction X‐Ray Detector with Ultra‐Low Detection Limit

Abstract Metal halide perovskite (MHP) single crystals have shown great potential for high‐performance X‐ray detection due to their excellent carrier transport properties, tunable optical bandgap, and low‐temperature fabrication process. However, 3D perovskite single crystals suffer from severe ion migration, limiting the stability and sensitivity of X‐ray detectors. Herein, a lowing temperature crystallization (LTC) method for liquid‐phase epitaxial growth of 2D (PEA)₂PbBr₄ single‐crystal (SC) film on 3D CsPbBr₃ substrate is demonstratedand a 2D/3D (PEA)₂PbBr₄/CsPbBr₃ SC heterojunction is successfully constructed. The epitaxial (PEA)₂PbBr₄ layer shows a pronounced passivation effect on CsPbBr₃ SC with a low trap density of 2.27 × 10¹⁰ cm⁻³. As such, the prepared 2D/3D heterojunction X‐ray detector achieves a record‐low detectable dose rate of 3.05 nGy_air s⁻¹ and high sensitivity of 34496 µC Gy_air⁻¹ cm⁻² in 120 keV hard X‐ray detection, with a largely suppressed dark current drift of 2.49 × 10⁻⁴ nA cm⁻¹ s⁻¹ V⁻¹. In addition, the heterojunction detector exhibits a self‐driven sensitivity of 44 µC Gy_air⁻¹ cm⁻² due to its built‐in electric field. This work provides a simple strategy to controllable construct 2D/3D MHP SC heterojunction with excellent optoelectronic characteristic, which is conducive to promoting the development of MHP SC X‐ray detectors and other optoelectronic devices.