PF₆⁻ Pseudohalides Anion Based Metal‐Free Perovskite Single Crystal for Stable X‐Ray Detector to Attain Record Sensitivity

Abstract 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.