Fluorophenylalkylamine passivation of α-FAPbI₃ for high-performance and air-stable photodetectors

Formamidinium–lead triiodide (FAPbI₃) shows strong potential for high-performance photodetectors owing to its narrow band gap and superior thermal stability. However, fabrication of pure-phase α-FAPbI₃ via a simple method remains challenging. Herein, a facile strategy based on antisolvent engineering is introduced to obtain pure-phase FAPbI₃ perovskite films by incorporating 3,5-difluorobenzylamine (DFBZ) into one-step antisolvent chlorobenzene. The findings reveal that the DFBZ molecule can effectively control the crystallization of perovskite and improve α phase stability of FAPbI₃ perovskite. The perovskite films incorporating DFBZ exhibit a more uniform and denser surface morphology as well as prolonged carrier lifetime. The resulting photodetectors demonstrate a broad spectral response from 300 to 850 nm, with a responsivity of up to 0.49 A·W⁻¹ at 770 nm. The DFBZ molecule can effectively passivate perovskite crystal defects and also improve the stability of perovskite films. The optimized devices retain approximately 90% of their initial performance after storage in air environment of 25 °C and a relative humidity of 30% for 400 h. The strategy provides an effective route to prepare stable pure-phase α-FAPbI₃ perovskite films and broadband photodetectors.