Ab Initio Study of Structural, Electronic, Optical, and Thermoelectric Properties of Cs<sub>2</sub>(Li/Na)GaI<sub>6</sub> for Green Energy Applications
Mukaddar Sk, Gourav Gourav, Saurabh Ghosh
Abstract
The recent year has witnessed a flurry of activities in investigating the promising electronic, optical, and transport properties of lead‐free double perovskite halides. In the present work, the structural, electronic, optical, and transport properties of Cs 2 (Li/Na)GaI 6 are carefully examined. The predicted negative formation energy, absence of imaginary frequency in the phonon spectra, and ab‐initio molecular dynamics calculations show that they are thermodynamically stable. Additionally, electronic studies employing generalized gradient approximation (GGA)–Perdew–Burke–Ernzerhof (PBE) + modified Becke‐Johnson + spin‐orbit coupling reveal that Cs 2 (Li/Na)GaI 6 exhibits a direct bandgap, with values of 1.24 eV for Cs 2 LiGaI 6 and 1.39 eV for Cs 2 NaGaI 6 . The exceptional optical properties, including a high absorption coefficient (10 5 cm −1 ) and excellent optical conductivity with low reflectivity across the entire UV–visible range, indicate that Cs 2 (Li/Na)GaI 6 are promising materials for solar cell applications. Moreover, the ultralow thermal conductivity, high Seebeck coefficient, and substantial electrical conductivity of Cs 2 (Li/Na)GaI 6 result in a high figure of merit over the temperature range of 200–600 K. Thus, Cs 2 (Li/Na)GaI 6 shows strong potential as both photovoltaic and thermoelectric materials.