Construction of 2D-3D Halide Perovskite Heterojunctions with the Amine Vapor Replacement Reaction

2D/3D perovskite-based X-ray detectors have emerged as one of the most competitive candidates for future medical imaging owing to their ease of fabrication via solution processes and outstanding performance. Nevertheless, despite significant efforts in innovating materials and device structures, it remains challenging to achieve high-quality 2D/3D heterojunctions with a single and effective strategy. In this study, we propose a gas-phase replacement reaction between propylamine (PA) and MAPbBr₃ for the construction of the 2D (PA)₂PbBr₄-3D MAPbBr₃ heterojunction. The growth of the (PA)₂PbBr₄ layer was influenced by the diffusion of PA. The quality of (PA)₂PbBr₄ could be controlled by finely choosing reaction conditions. X-ray detectors based on optimized 2D-3D perovskite heterojunctions showed a sensitivity of 25,143 μC Gy_air ^-1 cm^-2, lowest limit of detection of 1.33 μGy_air s^-1, dark current drift value of 2.27 × 10^-3 nA cm^-1 s^-1 V^-1, and outstanding performance, which are all better than those of detectors based on MAPbBr₃ single crystals. This research unveils the growth mechanism of 2D (PA)₂PbBr₄ perovskite via gas-phase replacement reactions, which are beneficial for the construction of high-quality 2D/3D perovskite-based heterojunctions.