Interlayer-Spacing Engineering of Lead-Free Perovskite Single Crystal for High-Performance X-Ray Imaging

Lead-free A₃ Bi₂ I₉ -type perovskites are demonstrated as a class of promising semiconductors for high-performance X-ray detection due to their high bulk resistivity and strong X-ray absorption, as well as reduced ion migration. However, due to their long interlamellar distance along their c-axis, their limited carrier transport along the vertical direction is a bottleneck for their detection sensitivity. Herein, a new A-site cation of aminoguanidinium (AG) with all-NH₂ terminals is designed to shorten the interlayer spacing by forming more and stronger NH···I hydrogen bonds. The prepared large AG₃ Bi₂ I₉ single crystals (SCs) render shorter interlamellar distance for a larger mobility-lifetime product of 7.94 × 10^-3  cm²  V^-1 , which is three times higher than the value measured on the best MA₃ Bi₂ I₉ SC (2.87 × 10^-3  cm²  V^-1 ). Therefore, the X-ray detectors fabricated on the AG₃ Bi₂ I₉ SC exhibit high sensitivity of 5791 uC Gy^-1  cm^-2 , a low detection limit of 2.6 nGy s^-1, and a short response time of 690 µs, all of which are far better than those of the state-of-the-art MA₃ Bi₂ I₉ SC detectors. The combination of high sensitivity and high stability enables astonishingly high spatial resolution (8.7 lp mm^-1 ) X-ray imaging. This work will facilitate the development of low-cost and high-performance lead-free X-ray detectors.