In this study, a high-performance photodetector comprised of formamidinium
cesium lead iodide (FA1−xCsxPbI3) thin film is developed. The Cs-doped FAPbI3
perovskite material is synthesized through a simple spin-coating method,
via which FA1−xCsxPbI3 with different Cs doping levels (x = 0.1, 0.15, 0.2, and
0.3) can be obtained. Further optoelectronic characterization reveals that the
FA0.85Cs0.15PbI3 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 Hz1/2 W–1,
respectively. It is also worth noting that the present perovskite photodetector
demonstrates an ultrafast response speed (tr/tf: 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 FA1−xCsxPbI3 an
idea material for high-performance photodetectors application.