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Double perovskite halides Cs2TlGaCl6 and Cs2TlGaBr6 are promising for photovoltaic applications due to their optoelectronic properties. The first-principles density functional theory (DFT) with the HSE06 hybrid functional was applied to systematically investigate their structural stability, electronic structure, optical absorption, and mechanical properties. The calculated tolerance and octahedral factors confirm stable crystal structures. The indirect band gaps of 2.50 eV (Cs2TlGaCl6) and 1.54 eV (Cs2TlGaBr6) are suitable for visible-light harvesting. Strong visible-light absorption and low reflectivity are observed. Elastic constant calculations based on the Voigt–Reuss–Hill approximation validate mechanical stability. The Spectroscopic Limited Maximum Efficiency (SLME) estimates promising photovoltaic efficiencies of 12.41% for Cs2TlGaCl6 and 29.73% for Cs2TlGaBr6 perovskite. These findings highlight the potential of Cs2TlGaCl6 and Cs2TlGaBr6 for low-cost, high-efficiency solar cells, warranting further experimental investigations. [ABSTRACT FROM AUTHOR]

In this study, we employ density functional theory to investigate KXH3 (X = Ca, Sc, Ti, & Ni) hydride perovskites for H2 storage applications. Lattice parameters calculated using GGA-PBE are 4.482 Å, 4.154 Å, 3.974 Å, and 3.686 Å for KCaH3, KScH3, KTiH3, and KNiH3, respectively. Electronic structure analysis shows KScH3, KTiH3, and KNiH3 are metallic, while KCaH3 is a semiconductor. Strong bonding and long bond lengths indicate high hydrogen storage potential. The materials exhibit thermodynamic and mechanical stability, suggesting feasibility for experimental synthesis. Gravimetric analysis reveals promising hydrogen storage capacities: 3.646 wt% (KCaH3), 3.452 wt% (KScH3), 3.346 wt% (KTiH3), and 3.005 wt% (KNiH3). Calculated hydrogen desorption temperatures range from 442.40 K to 614.82 K, indicating suitability for practical hydrogen storage applications. These findings highlight the potential of KXH3 (X = Ca, Sc, Ti, & Ni) perovskites as effective hydrogen storage materials. [ABSTRACT FROM AUTHOR]