Orthorhombic CsPbI₃ Inorganic Perovskite: DFT Insights into Its Mechanical and Optical Properties

We present Density Functional Theory (DFT) study of the multifaceted properties of CPbI₃, an inorganic perovskite semiconductor, with a particular focus on its potential in photovoltaic applications. We systematically analyze the interplay between its structural, mechanical, electronic, and optical characteristics, considering their relevance to solar cell technology. Utilizing the linearized extended plane wave method (FP-LAPW) as implemented in Wien2K, we conduct a comparative assessment of our findings, obtained through distinct DFT approximation methods, including the local density approximation (LDA), generalized gradient approximation (GGA), and the modified Becke–Johnson potential (mBJ). Our investigation establishes that the orthorhombic phase is energetically most favorable compared to the cubic phase (convex Hull is ~0.03eV/atom), while both phases demonstrate mechanical stability and synthetic feasibility based on elastic tensor and lattice vibration calculation. Additionally, the band structure reveals the presence of an indirect bandgap of 1.2eV (GGA) that is increases to 2.1eV in mBJ calculations. Furthermore, we calculate and interpret essential optical parameters such as optical conductivity, index of refraction, dielectric constant. Our comprehensive analysis leads us to the conclusion that both the cubic and orthorhombic phases of CsPbI₃ hold substantial promise as optoelectronic materials that warrant further research and development.