Effects of cesium content on the triple-cation lead halide perovskite photodetectors with enhanced detectivity and response time

•A (FA0.75MA0.25)1−xCsxPbI3 film was fabricated by the one-step process.•A 5% CsI doping is the optimized amount for improving FA0.75MA0.25PbI3 film.•The FA-MA-Cs triple-cation lead halide perovskite photodetectors with enhanced detectivity and response time.•Performance of perovskite halide based photodetector with different Cs doping concentration.•When 5% Cs-doped sample showed an optimal performance, resulting from the improved material and optical properties. [Display omitted] This research reports on the effects of Cs doping in the Csx(FA0.75MA0.25PbI3)1−x based perovskites and photodetectors (PDs) with various Cs contents from 0% to 7.5%. The incorporation of 2.5–5% Cs markedly improved the crystal quality of perovskite films that in turns increased, the photoluminescence, absorbance, and quantum efficiency. Over-doping Cs upto 7.5% degraded the devices. X-ray photoemission spectroscopy shows that the binding energies of the Cs, Pb and I core levels shifted to high-energy side, indicating the Cs enter the lattice sites and improved the stability of the film. For PD applications, the influence of Cs doping in the perovskite was mostly on the reduction of rise time, causing by increase of the generation rate of carriers and reduction of trap densities of carriers. The 5% Cs-doped sample showed the best performance, because of the optimization of the grain size, crystal quality and trap density. As a result, the self-powered perovskite demonstrated an impressive performance with ~70% external quantum efficiency, 0.36 A W−1 responsivity, 1.15 × 1012 Jones, and rapid rise and decay time of 1.5 μs and 21 μs, respectively.