Influence of 5‑ammonium valeric acid iodide additive on the structural and optical behaviors of methylammonium lead tri-iodide perovskite thin films

Methylammonium lead tri-iodide, (AVAI)_x(MAPbI₃)_1-x (x = 0, 0.05, 0.1, 0.15, 0.25) perovskite thin films were formed using a spin coating method in a glove box beneath an argon environment. The structures of the formed films were investigated using the X-ray diffraction technique. The effect of AVAI amount on the intensity of diffraction peaks was explored. Film with 15% AVAI has the highest optical absorbance. The transmittance of the film 25% AVAI was enhanced as compared with undoped film in the wavelength range up to 1700 nm but it decreased beyond this range. The optical band gap energy (E_g) value of MAPbI₃ is 1.58 eV. The direct and indirect E_g values of the films became 1.52–1.59 or 1.31–1.49 eV depending on the amount of AVAI on the films, respectively. Various specified models were used to determine the refractive index (n) of different films. The n-average rose from 2.95 (based on direct E_g value) or 2.99 (based on indirect E_g) for the ​ film (x = 0) to 2.98 (based on direct E_g value) or 3.08 (based on indirect E_g) for the film with 15% AVAI. Film with 15% AVAI has the highest dielectric value, while film with 25% AVAI has the maximum dielectric loss value as compared with MAPbI₃ and other dopant ratios. Film with 25% AVAI has the highest optical conductivity value. The film with 15% AVAI showed significant gains in nonlinear optical (NLO) parameter values, making it a suitable option for a variety of NLO and future photonic uses. We studied the photoluminescence features of different films using a 532 nm laser excitation wavelength.