Co‐Firing Slow Solidification Process for Growing Indium‐Doped C s 3 C u 2 I 5 Single Crystals With Record‐Breaking X‐Ray Detection Performance

Perovskite single crystals have shown great potential in both direct and indirect X‐ray detection. In direct detection, high leakage current and response drift caused by low resistivity and severe ion migration will lead to low device sensitivity and stability. In indirect detection, the reabsorption behavior and afterglow phenomenon caused by edge transitions in the scintillator will seriously damage its scintillation performance, thereby limiting the high‐quality imaging of the detector at low doses. Herein, we demonstrate a brand‐new co‐firing slow solidification process to prepare large‐sized In‐doped Cs 3 Cu 2 I 5 single crystals for direct and indirect detection. The regular‐shaped Cs 3 Cu 2 I 5 : In wafer used for indirect detection achieves a light yield of 74 368 Ph MeV −1 , which is the highest related to indium‐doped Cu‐based perovskites. The controlled cooling Cs 3 Cu 2 I 5 : In single crystals, achieve a detection limit of 29.98 nGy s −1 and a spatial resolution of 15.1 lp mm −1 . We further fabricate a direct X‐ray detector with a vertical structure of Au/Cs 3 Cu 2 I 5 : In single crystal/Cu. The resistivity of the detector prepared by controlled cooling is 1.43 × 10 11 Ω × m, which is three orders of magnitude higher than that of the detector obtained by natural cooling (2.55 × 10 8 Ω × m). Meanwhile, under an electric field of 100 V mm −1 , the sensitivity of the controlled cooling detector is 4507 μC Gy −1 cm −2 , 188% higher than that of the natural cooling detector (2392 μC Gy −1 cm −2 ). These results prove that our process will provide new insights into high‐sensitivity X‐ray detection and low‐dose X‐ray imaging.