Halide-modulated self-assembly of metal-free perovskite single crystals for bio-friendly X-ray detection

Not until recently have metal-free halide perovskites become recognized as novel candidates for ferroelectrics and X-ray detection. However, molecular self-assembly of these perovskites and its influence remain unexplored. Here, we prepare large high-quality DABCO-NH4X3 (DABCO = N-N′-diazabicyclo[2.2.2]octonium, X = Cl, Br, I) single crystals and demonstrate the understandings of how halide-modulated molecular assembly affects their crystal packing, band nature, mechanical and electrical properties, and final optoelectronic performance. In this series, the 1D crystal packing and low carrier effective masses endow superior in-plane charge transport for the I-based crystal. As such, higher carrier mobility (110 versus ∼10–20 cm2 V−1 s−1) and longer charge diffusion length (∼90 versus ∼50 μm) are achieved in contrast to the Cl- and Br-based analogs. The excellent charge transport properties finally translate to highly efficient X-ray detection and imaging for the I-based crystal detector, with a sensitivity up to 567 μC Gyair−1 cm−2 and a well-defined “heart” X-ray image. © 2021