Investigation of Two‐Dimensional Ruddlesden–Popper BZA ₂ PbX ₄ (X = I, Br, and Cl) and Mixed‐Halides BZA ₂ PbBr _x Cl _{4− x} Perovskites: Opto‐Electromechanical, Thermodynamic Properties, Moisture, and Strain Effects

Herein, the properties of BZA ₂ PbX ₄ (X = I, Br, and Cl) and mixed halides BZA ₂ PbBr _x Cl _{4‐ x} ( x = 1, 2, and 3) perovskites are comprehensively investigated, utilizing density functional theory (DFT). As there has been no prior comprehensive study on the substantial characteristics of mixed halides and the distinctive features of BZA ₂ PbI ₄ , BZA ₂ PbBr ₄ , and BZA ₂ PbCl ₄ using DFT, a significant gap in the existing literature is addressed. The optical and electronic properties, band structures, band edge orbitals, and effective masses with and without spin‐orbit coupling effects are analyzed. The investigation also examines the impact of strain (tensile and compressive) on the properties of these materials. It is revealed that among the investigated compounds, BZA ₂ PbCl ₄ emerges as the most thermodynamic and moisture stable. This trend is corroborated by the energy fluctuation, with BZA ₂ PbCl ₄ demonstrating a narrower range, indicative of superior thermal stability. Furthermore, Voigt–Ruess–Hill approximations indicate that the mechanical moduli increase as the halide changes from I to Cl. Moreover, BZA ₂ PbI ₄ exhibits the highest level of disorder, whereas BZA ₂ PbCl ₄ has the lowest entropy value at the same temperature. The results highlight that these materials emerge as promising candidates for applications in the active layer of perovskite light‐emitting diodes and optoelectronic devices.