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

Abstract Lead‐free A₃Bi₂I₉‐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 AG₃Bi₂I₉ 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 MA₃Bi₂I₉ SC (2.87 × 10⁻³ cm² V⁻¹). Therefore, the X‐ray detectors fabricated on the AG₃Bi₂I₉ 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 MA₃Bi₂I₉ 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.