<p>In present work aims to construct of (5-Ammonium valeric acid iodide)_<i>x</i>(FA)_1−<i>x</i>PbI₃ films as a promising films to utilize in solar cells and linear/nonlinear optical applications. The films were fabricated employing the spin coating procedure under argon atmosphere. The influence of the amount of 5-Ammonium valeric acid iodide (AVAI) on the stability of FAPbI₃ films was studied employing X-ray diffraction device. By incorporating AVAI into the films, the perovskite’s high crystallinity is enhanced, leading to an increase in stability. The impact of the AVAI doping amount on the absorbance and transmittance spectra of FAPbI₃ films was carried out. Films containing 25% AVAI have the smallest optical band gap energy (<i>E</i>_g) value of 1.5&#xa0;eV. Several empirical models were employed to compute the different films’ refractive indices (<i>n</i>) based on the <i>E</i>_g value. Adding 25% of AVAI to the film caused the n-average to rise from 2.939 for the film with <i>x</i> = 0 to 2.95. The impact of AVAI ratio on the dielectric constant, energy loss functions, and optical conductivity of different films were explored. Films containing 25% AVAI displayed the largest real component of the dielectric constant (<i>ε</i>_r) value, whereas the film with 0% AVAI demonstrated the largest imaginary component of the dielectric constant (<i>ε</i>_i) value compared to FAPbI₃ and other doping ratios. A film containing 15% AVAI demonstrated the lowest <i>ε</i>_i, surface energy loss functions (SELFs), and volume energy losses (VELFs) values. Films without AVAI revealed the greatest optical conductivity value. The films showed the highest nonlinear optical parameter values when AVAI reached 25%. The improvement in photoluminescence intensity as the amount of AVAI increased in the films indicated a drop in nonradiative recombination losses, a lessening in defect states, and an elevation in the crystallinity of the samples, as revealed using the XRD technique.</p>