<p>A-site bandgap engineering is the process of changing a material’s electronic band structure by adjusting or replacing the A-site cation in a perovskite material. This method is extremely beneficial when tailoring the optoelectronic, photovoltaic, and hydrogen storage capabilities of perovskite material. In this work, we used the first-principles analysis to study the optoelectronic and hydrogen storage ability of alkali-based Z₂TlGaH₆ (Z = Li, Na, K, Rb) perovskite hydrides. A semi-local exchange potential is employed to parametrize the exchange–correlation interactions. The structural scrutiny of the studied hydrides reveals complete stability. The elastic constants elaborate that the Rb₂TlGaH₆ possess higher resistance to compressional forces as compared to Li₂TlGaH₆, Na₂TlGaH₆, and K₂TlGaH₆. Pugh’s and Poisson’s ratio and the Cauchy’s pressure reveals that the studied hydride remains ductile as “Li” is replaced by “Na”, “K” and “Rb” at A-site in Z₂TlGaH₆. From the electronic properties it is noticed that all hydrides possesses indirect bandgaps of 1.04&#xa0;eV (Li₂TlGaH₆), 1.22&#xa0;eV (Na₂TlGaH₆), 1.44&#xa0;eV (K₂TlGaH₆) and 1.45&#xa0;eV (Rb₂TlGaH₆). The materials interaction with the electromagnetic radiations reveals that the studied hydrides exhibit high polarization, dispersion, absorption in the ultraviolet and visible region. The hydrogen storage capacities reveal that Li₂TlGaH₆ is the better candidate for compact hydrogen storage because it has the largest volumetric and gravimetric hydrogen density as compared to Na₂TlGaH₆, K₂TlGaH₆, and Rb₂TlGaH₆. Our results demonstrate that the studied hydrides are strong candidates for future renewable energy technologies.</p>