PF 6 - Pseudohalides Anion based Metal-Free Perovskite Single Crystal for Stable X-ray Detector to Attain Record Sensitivity.

Metal-free perovskites (MFPs) possess excellent photophysical properties of perovskites while avoiding the introduction of toxic metal ions and organic solvents, and have been expanded to X-ray detection. However, iodine-based high-performance MFPs are tended to oxidation, corrosion and uncontrolled ion migration, resulting in poor material stability and device performance. Herein, the strongly electronegative PF 6 - pseudohalide is used to fabricate the large-size MDABCO-NH 4 (PF 6 ) 3 (MDBACO = methyl-N'-diazabicyclo[2.2.2]octonium) single crystals (SCs) for solving the problems of iodine ions. After the introduction of PF 6 - pseudohalides, the Coulomb interaction and hydrogen bonding strength are enhanced to alleviate the ion-migration and stability problems. Moreover, combined with theoretical calculations, PF 6 - pseudohalides increase the ion-migration barrier, and affect the contribution of its components to energy band for a broadening band gap. Meanwhile, the improved physical properties, such as large activation energy of ionic migration, high resistivity and low current drift, further expand its application in low-dose and sensitive X-ray detection. Finally, the X-ray detector based on MDABCO-NH 4 (PF 6 ) 3 SCs achieves a sensitivity of 2078 μC Gy air -1 cm -2 (highest among metal-free SCs-based detectors) and the lowest detectable dose rate (16.3 nGy air s -1 ). This work has expanded the selection of MFPs for X-ray detectors and somewhat advanced the development of high-performance devices. This article is protected by copyright. All rights reserved.