The remarkable electrical and optical properties of lead halide perovskites have made them potential materials for next-generation optoelectronic applications. This work uses first-principles density functional theory using Quantum Espresso to conduct a thorough theoretical investigation of the electro-optical properties of hybrid and inorganic perovskites FAPbX₃ and CsPbX₃ (X = Cl, Br, I). Through geometry optimization, the compounds' structural stability is examined, yielding accurate equilibrium lattice parameters for ensuing electronic and optical computations. All compositions show a direct band gap nature, with the band gap values largely reliant on the halide anion, according to calculations of the electronic band structure and density of states. The adaptability of these materials for optoelectronic design is demonstrated by the continuous band gap tuning from the ultraviolet to the visible range made possible by systematic halide replacement.

Calculations of the frequency-dependent dielectric function, absorption coefficient, refractive index, reflectivity, and optical conductivity are used to assess optical characteristics. The findings show a high dielectric response and significant optical absorption in the visible spectrum, suggesting effective light–matter interaction. Lattice expansion and stronger orbital hybridization are responsible for the slightly reduced band gaps and improved optical absorption of FAPbX₃ perovskites when compared to their inorganic counterparts CsPbX₃, according to a comparative analysis. It is discovered that the electro-optical response is extremely sensitive to the halide composition, providing a feasible route for band gap engineering and optimizing optical performance. Furthermore, the calculated optical parameters indicate favorable transparency–absorption trade-offs, which are crucial for efficient optoelectronic device performance. The present theoretical results are expected to serve as a useful reference for future experimental validation and material optimization. This study thus contributes to a deeper understanding of structure–property relationships in lead halide perovskites from a purely first-principles perspective. All things considered, this first-principles investigation offers basic understanding of the electrical structure and electro-optical behavior of FAPbX₃ and CsPbX₃ perovskites. The results highlight the promise of inorganic and hybrid lead halide perovskites for use in photovoltaics, light-emitting devices, and photodetectors and provide theoretical direction for the logical design of high-performance optoelectronic materials.