Effect of cesium doping and antisolvent on the linear and nonlinear characteristics of CH₃NH₃PbI₃ perovskite thin films

Cesium (Cs) doped methylammonium lead iodide thin films (MA_1-xCs_xPbI₃, x = 0, 0.03, 0.05, 0.1) were formed using the spin-coated method in a dry air atmosphere. The effect of Cs doping and chlorobenzene (CB) on the crystallinity of the films was investigated using X-ray diffraction technique. The influence of doped Cs amount and adding CB during the preparation of the films on the transmittance, reflectance, absorption coefficient, skin depth, real and imaginary parts of the dielectric constant, and photoluminescence emission of the films were explored. The films' refractive indices showed normal and abnormal dispersion in different parts of the spectra. The optical bandgap of the films depends on the amount of Cs doping. The optical bandgap of the films prepared without CB is less than that of the corresponding films formed with CB. The surface energy loss function and the volume energy loss function exhibited similar behavior, where the energy lost by electrons traveling in the material is higher than the energy lost by electrons moving on the surface. The nonlinear optical behavior was enhanced for the thin films doped with 10% Cs (without CB) or 5% Cs (with CB). The DC-dark conductivity measurements for all samples were also performed.