Bifunctional polymer assisted growth of crack-free thick perovskite films for flexible X-ray detection

The expanding use of perovskite materials in flexible optoelectronics has sparked growing interest in their application for flexible X-ray detectors. Achieving thick perovskite films is crucial for effective X-ray absorption; however, such films typically exhibit brittleness and crack formation. In this work, we present a bifunctional polymer-assisted approach employing the triblock copolymer Pluronic P123, composed of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG), to simultaneously control crystallization and enhance the mechanical integrity of lead-free Cs₂AgBiBr₆ (CABB) thick films. The PEG segments coordinate selectively with Ag⁺ ions, guiding evolution to the stable 3D phase, while the PPG segments introduce steric effects that mitigate excessive Ag⁺ coordination and favor uniform crystal growth. This cooperative mechanism yields crack-free, highly crystalline, and mechanically flexible perovskite films. The resulting P123-modified CABB detectors demonstrate a remarkable X-ray sensitivity of 244.71 µC Gy^-1 cm^-2 and low detection limit of 121 nGy s^-1 under a low bias of 50 V mm^-1, over twice that of unmodified devices. Moreover, the modified detectors maintained over 70% of their initial sensitivity under small bending radii and over 80% after 500 bending cycles, exhibiting outstanding fatigue endurance and long-term stability over a 60-day period, in contrast to the pronounced degradation seen in pristine CABB devices. This study establishes a polymer-guided design paradigm for fabricating lead-free, flexible, and scalable perovskite-based radiation detectors.