In Situ Regulating the Order–Disorder Phase Transition in Cs2AgBiBr6 Single Crystal toward the Application in an X-Ray Detector

The double perovskite Cs 2 AgBiBr 6 single crystal holds great potential for detecting applications because of its low minimum detectable dose rate and toxic-free merit. Nevertheless, the disordered arrangement of Ag + /Bi 3+ usually gives rise to unexpected structural distortion and thereafter heavily influences the photoelectric properties of the Cs 2 AgBiBr 6 single crystal. Herein, phenylethylamine bromide is demonstrated to be capable of in situ regulation of the order–disorder phase transition in the Cs 2 AgBiBr 6 single crystal. The improved ordering extent of alternatively arranged [AgX 6 ] 5− and [BiX 6 ] 3− octahedra is theoretically and experimentally proven to decrease the defect density and suppress self-trapped exciton formation, and thereby tune the band gap and enhance the carrier mobility, which consequently promotes its application in an X-ray detector. The performance of a corresponding detector based on PEA-Cs 2 AgBiBr 6 single crystal displays superior performances, e.g., longer carrier drift distance, higher photoconductive gain, and faster current response (13 vs 3190 µs). Prominently, the as-fabricated PEA-Cs 2 AgBiBr 6 single-crystal X-ray detector has an extremely high sensitivity with a value of 288.8 µC Gy air −1 cm −2 under a bias of 50 V (22.7 V mm −1 ), which largely outperforms those of their counterparts with lower ordering structure.