Unveiling Thermal, Phonon, and Optoelectronic Characteristics of Cs ₃ O <i>X</i> ( <i>X</i>  = Cl, Br, or I) Antiperovskites for Sustainable Energy Applications: A DFT Exploration

This investigation explores the general characteristics, including the structural, electronic, mechanical, optical, thermal, and phonon properties of Cs 3 O X ( X = Cl, Br, or I) antiperovskite, incorporating the density functional theory (DFT). The motive behind this study is to comprehensively understand the behaviors of Cs 3 O X ( X = Cl, Br, or I) and to identify suitable applications according to its properties. Additionally, these compounds are lead‐free and nontoxic compounds, which are not harmful to the environment. This study finds that Cs 3 OCl, Cs 3 OBr, and Cs 3 OI have bandgap values of 0.159, 0.278, and 0.205 eV by using the generalized gradient approximation‐Perdew– Berke–Ernzerhof (GGA‐PBE) functional, as well as 1.719, 1.814, and 1.516 eV by using the hybrid‐HSE06 functional, respectively. The band gaps have significantly influenced the optical and mechanical properties of the compounds. In the visible range, the highest peaks of α lie between 0.5 × 10 4 and 1 × 10 4 1/cm for all three compounds, which is appropriate for a solar cell absorber. Besides, Cs 3 OI shows the largest elastic modulus of 21.21 GPa, which also has the highest bulk and shear modulus. The thermodynamic properties of Cs 3 O X ( X = Cl, Br, or I) have been affected by the changes in halogens such as with increasing halogen size enthalpy, entropy, and heat capacity have increased, whereas free energy and Debye temperature have decreased. Halogen size also affected the structural properties including the bond length and volume. A positive phonon frequency has been observed in Cs 3 OI while investigating the phonon characteristics, which indicates its dynamic stability, but Cs 3 OCl and Cs 3 OBr have shown a negative phonon frequency which denotes the dynamic instability. Considering its exceptional features, Cs 3 O X (where X = Cl, Br, or I) has the potential to be utilized in a wide range of applications, encompassing solar cell absorbers, optoelectronics, LED, and more.