Epitaxial Engineering of FAPbBr<sub>3</sub>/FAPbBr<sub>3–<i>x</i></sub>Cl<sub><i>x</i></sub> Heterojunctions\nfor Sensitive X‑ray and α‑Particle Detection

Halide\nperovskite crystals have attracted extensive research in\nthe field of radiation detection, thanks to their superior carrier\ntransport abilities and facile solution preparation methods. However,\ndark current instability is common in perovskite single-crystal devices,\nespecially under high bias voltages. Herein, we achieve the modulation\nof surface defects by epitaxial growth to obtain heterogeneous crystals\nwith high crystalline quality, developing FAPbBr<sub>3</sub>/FAPbBr<sub>3–<i>x</i></sub>Cl<sub><i>x</i></sub> heterojunctions\nto address severely increased dark current. The FAPbBr<sub>3</sub>/FAPbBr<sub>2.7</sub>Cl<sub>0.3</sub> heterojunction exhibits reduced\ntrap-state density and a significant built-in potential difference.\nBased on the effective utilization of the dark current cutoff effect\nof the heterojunctions, a dark current of 0.83 μA·cm<sup>–2</sup> is realized for the FAPbBr<sub>3</sub>/FAPbBr<sub>2.7</sub>Cl<sub>0.3</sub> detector, which is 7.5% of that based on\nan intrinsic FAPbBr<sub>3</sub> single crystal. Thus, an optimal sensitivity\nof 33612 μC·Gy<sub>air</sub><sup>–1</sup>·cm<sup>–2</sup> for Au/FAPbBr<sub>3</sub>/FAPbBr<sub>2.7</sub>Cl<sub>0.3</sub>/Au detector was achieved, at a bias of −250 V. Simultaneously,\nan energy resolution of 15.2% for <sup>241</sup>Am @ 5.49 MeV α-particle-induced\npulse height spectra was recognized. Our work not only establishes\na new benchmark for FAPbBr<sub>3</sub>-based perovskite performance\nbut also presents a pragmatic strategy to lower the harmful dark current\nin three-dimensional halide perovskite single crystals.