Several inorganic perovskites of iodine, bromine, and chlorine halides have emerged as candidates for various optoelectronic devices. High-quality CsPb(I1–xBrx)3 and CsPb(Br1–xClx)3 (x = 0.00, 0.25, 0.50, 0.75, and 1.00) inorganic perovskite thin films were prepared in this study using a thermal evaporation system. Experiments and first-principles calculations were conducted to elucidate the structural, electronic, and optical properties of the prepared films at room temperature. The thin-film perovskite band gap was tuned from 1.85 to 3.13 eV by replacing I– with Br– and then Cl–. Dominant excitonic effects on the onset of optical absorption led us to explicitly account for enhancing absorption through the Sommerfield factor, enabling us to extract the electronic band gap and the exciton binding energy correctly. We correlated our experimental results with the theory of first principles and gained insight into the lattice parameters, electronic structure, excitonic binding energy (Eb), dielectric constant (ε), and reduced effective mass (μ) of the carriers. With increasing concentration (x) of Br and Cl, the Eb increased from 39.44 meV for pure CsPbI3 to 63.04 and 96.73 meV for pure CsPbBr3 and CsPbCl3, respectively, because of a decrease in the dielectric constant and the almost constant value of μ at ∼0.051 me. The Urbach energy (EU) was calculated and found to fluctuate between 28 and 77 meV.