<p>Hybrid halide perovskites containing MA⁺ remain promising candidates for photovoltaic applications; however, their response to compositional modifications requires detailed analysis. In this work, first-principles calculations were employed to investigate the effect of partial A-site substitution in MA₀.₇₅AM₀.₂₅PbI₃ (AM = Cs, K, Na). Structural changes caused by octahedral cage distortion were examined, together with cohesive, substitution, and formation energy analyses. A comparative evaluation of the revTPSS, PBEsol, and PBE functionals was also performed to determine the electronic bandgap and related optical properties. The key findings of this study are: (i) octahedral distortion increases as the A-site ionic radius decreases; (ii) tolerance factors and formation energies indicate partial substitution (25%) is thermodynamically feasible; (iii) bandgap variations indicate that Cs- and K-substituted systems maintain suitable photoactive ranges, whereas Na substitution widens the gap (E_g &gt; 1.6&#xa0;eV) in all approximations; and (iv) optical parameters exhibit trends consistent with the electronic results, with no drastic variations induced by partial substitution of the organic cation. These results provide valuable insights into the understanding and rational design of alkali-metal-doped hybrid halide perovskites.</p> Graphical abstract <p></p>