Lead-free perovskite Cs2AgBiBr6/Cs3Bi2Br9 single-crystalline heterojunction X-ray detector with enhanced sensitivity and ultra-low detection limit

Lead-halide perovskite single crystal (SC) heterojunctions have attracted significant attention for X-ray detection owing to their unique combination of high sensitivity, resolution, stability and low detection limit. However, the toxicity of lead in those perovskite heterojunctions limits their practical applications. Herein, we report the construction of the first all-inorganic lead-free Cs 2 AgBiBr 6 /Cs 3 Bi 2 Br 9 SC heterojunctions with an area of 20 × 20 mm 2 via a facile liquid-phase epitaxial method through temperature-lowering crystallization. The epitaxial crystallization of the three-dimensional (3D) Cs 2 AgBiBr 6 SC film on a 2D Cs 3 Bi 2 Br 9 SC substrate requires a large driving force for transitioning from the Volmer–Weber mode to the layer-by-layer growth mode under a rapid cooling rate. The Cs 2 AgBiBr 6 /Cs 3 Bi 2 Br 9 SC heterojunction detector achieves a high sensitivity of 1390 µC Gy air −1 cm −2 for 100 keV hard X-ray detection at room temperature, which is enhanced to 2075 µC Gy air −1 cm −2 at 75°C, demonstrating impressive high-temperature stability. Moreover, the detector achieves a detection limit of 37.48 nGy air s −1 and excellent stability for 90 days without any encapsulation. This work demonstrates the feasibility of using the epitaxial mechanism of perovskite formation on a high-surface-energy substrate for the controllable construction of a 3D/2D heterojunction that significantly enhances X-ray detection performance.