Centimeter‐Sized Single Crystal of Two‐Dimensional Halide Perovskites Incorporating Straight‐Chain Symmetric Diammonium Ion for X‐Ray Detection

Two‐dimensional (2D) AA′ n −1 M n X 3 n +1 type halide perovskites incorporating straight‐chain symmetric diammonium cations define a new type of structure, but their optoelectronic properties are largely unexplored. Reported here is the synthesis of a centimeter‐sized AA′ n −1 M n X 3 n +1 type perovskite, BDAPbI 4 (BDA=NH 3 C 4 H 8 NH 3 ), single crystal and its charge‐transport properties under X‐ray excitation. The crystal shows a staggered configuration of the [PbI 6 ] 4− layers, a band gap of 2.37 eV, and a low trap density of 3.1×10 9  cm −3 . The single‐crystal X‐ray detector exhibits an excellent sensitivity of 242 μC Gy air −1  cm −2 under the 10 V bias (0.31 V μm −1 ), a detection limit as low as 430 nGy air  s −1 , ultrastable response current, a stable baseline with the lowest dark current drift of 6.06×10 −9  nA cm −1  s −1  V −1 , and rapid response time of τ rise =7.3 ms and τ fall =22.5 ms. These crystals are promising candidates for the next generation of optoelectronic devices.