Multistage Fluorination in a Metal‐Free Perovskite Ferroelectric Enables Multidirectional Self‐Powered X‐Ray Detection

Abstract

ABSTRACT Metal‐free perovskites (MFPs) have emerged as eco‐friendly candidates for next‐generation x‐ray detection. However, their development is severely hindered by poor material stability and the reliance on high driving voltages, which exacerbate device complexity and operational risks. Herein, we adopt a multistage fluorination strategy to develop a novel MFP ferroelectric, FMDABCO‐NH 4 (PF 6 ) 3 (FMDABCO 2+ = N ‐fluoromethyl‐ N′ ‐diazabicyclo[2.2.2]octonium). X‐site fluorination endows FMDABCO‐NH 4 (PF 6 ) 3 with excellent stability, while A‐site fluorination enhances molecular dipoles and rotational barriers, leading to multiaxial ferroelectricity, an elevated Curie temperature ( T C ) of 340 K, and a spontaneous polarization ( P s ) of 16 µC cm −2 , the highest value among reported fluorinated MFP ferroelectrics. As a result, FMDABCO‐NH 4 (PF 6 ) 3 single crystals enable self‐powered x‐ray detection along three equivalent polar axes, representing the first multiaxial self‐powered MFP x‐ray detector. Furthermore, under a low electric field of 80 V mm −1 , FMDABCO‐NH 4 (PF 6 ) 3 delivers a record‐high sensitivity of 2860 µC Gy air −1 cm −2 among MFP ferroelectrics, while retaining 93% of its initial sensitivity after 1 year of ambient exposure. This work establishes a viable pathway toward environmentally benign, high‐performance, and self‐powered x‐ray detectors.