PF₆ ^- 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 PF₆ ^- pseudohalide is used to fabricate the large-size MDABCO-NH₄ (PF₆ )₃ (MDBACO = methyl-N'-diazabicyclo[2.2.2]octonium) single crystals (SCs) for solving the problems of iodine ions. After the introduction of PF₆ ^- pseudohalides, the Coulomb interaction and hydrogen bonding strength are enhanced to alleviate the ion-migration and stability problems. Moreover, combined with theoretical calculations, PF₆ ^- pseudohalides increase the ion-migration barrier, and affect the contribution of its components to the energy band for a broadening bandgap. 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-NH₄ (PF₆ )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.