In this work, we adopted a rapid thermal processing (RTP) for selenization and studied the influence of selenization time on vacuum evaporated multi-stacked precursor’s to form Ag₂ZnSnSe₄ (AZTSe) thin films. The RTP selenization temperature, pre-annealing temperature and pre-annealing time were optimized in our previous study on Ag₂ZnSnSe₄ films and found to be 400 °C, 250 °C and 20 min, respectively. From energy-dispersive X-ray (EDX) study, the Ag/(Zn + Sn), Zn/Sn, and Se/metals ratios are observed to vary in the range (0.81–0.99), (1.13–1.62), and (1.03–0.94) with an increase in selenization time from 1 to 5 min, respectively. The multi-stacked thin films selenized at 400 °C for 1 min was found to be nearly stoichiometric. The photoelectron spectroscopic analysis reveals that the elements Ag, Zn, Sn, and Se exhibit + 1, + 2, + 4, and -2 oxidation states, respectively. The X-ray diffraction (XRD) study shows the formation of single-phase AZTSe with (112) plane as a strong orientation for 1-min RTP selenization. Morphological studies reveal the growth of larger grains with a mean grain size of ~ 0.5 µm. It was observed that the AZTSe thin film grown with 1-min RTP selenization has an optical band gap of 1.37 eV. These films have electrons as a majority charge carrier (n-type) with highest mobility and resistivity values of 79.4 cm²(Vs)⁻¹ and 2.61 × 10⁴ Ωcm, respectively. The numerical simulation was carried out on p-CZTSe/n-AZTSe-based solar cells with the obtained experimental data of AZTSe films in the present study using Solar Cell Capacitance Simulator (SCAPS-1D) software, and it shows the maximum power conversion efficiency (ƞ) of 16.84%.