Broadband, Ultrafast, Self‐Driven Photodetector Based on Cs‐Doped FAPbI₃ Perovskite Thin Film

Abstract In this study, a high‐performance photodetector comprised of formamidinium cesium lead iodide (FA_1−xCs_xPbI₃) thin film is developed. The Cs‐doped FAPbI₃ perovskite material is synthesized through a simple spin‐coating method, via which FA_1−xCs_xPbI₃ with different Cs doping levels (x = 0.1, 0.15, 0.2, and 0.3) can be obtained. Further optoelectronic characterization reveals that the FA_0.85Cs_0.15PbI₃ photodetector exhibits reproducible sensitivity to irradiation with wavelengths in the range from 240 to 750 nm, whereas it is weakly sensitive to wavelengths longer than 750 nm. The responsivity and specific detectivity are estimated to be around 5.7 A W⁻¹ and 2.7 × 10¹³ cm Hz^1/2 W^–1, respectively. It is also worth noting that the present perovskite photodetector demonstrates an ultrafast response speed (t_r/t_f: 45 ns/91 ns) at zero bias voltage, which is probably related to the ultrafast lifetime and high quality of thin film according to the Hall effect study. Finally, this device shows a weak degradation in sensitivity to white light after storage at ambient condition for 45 days. The totality of the broadband sensitivity, high specific detectivity, ultrafast response speed, and self‐driven property renders the FA_1−xCs_xPbI₃ an idea material for high‐performance photodetectors application.