Insight into structural, Opto-electronic and elastic properties of lead-free double perovskites Cs2TlInX6 (X = Cl, Br and I) for optoelectronic applications: A first principles calculations

In recent years, lead-free double perovskites have gained attention due to their potential in optoelectronics. This study investigates the structural, electronic, mechanical and optical properties of Cs2TlInX6 (X = Cl, Br, I) using first-principles calculations. Structural optimizations reveal increasing lattice constants (11.05 & Aring;-12.28 & Aring;) with larger anions, while band structure analysis indicates indirect band gaps of 3.52 eV, 2.49 eV and 1.45 eV for Cl, Br, and I variants suitable for visible to ultra-visible applications. Mechanical analysis confirms structural stability with Cs2TlInCl6 exhibiting the highest bulk modulus (28.3 GPa) and Cs2TlInI6 demonstrating enhanced flexibility. Optical assessments show significant light absorption with Cs2TlInI6 possessing the highest dielectric constant (4.05). These findings highlight the potential of Cs2TlInX6 as stable, tunable, and highly absorptive materials, making them promising candidates for next-generation photovoltaic and optoelectronic applications.