Comprehensive DFT and SCAPS-1D Study of Structural, Electronic, Optical, Mechanical, Phonon, Thermoelectric, and Photovoltaic Properties of Lead-Free Z3BrO (Z = K, Rb, Cs, and Fr) Anti-Perovskites.

This study presents a comprehensive first-principles and device-performance investigation of alkali metal-based anti-perovskites Z3BrO (Z = K, Rb, Cs, and Fr) for advanced optoelectronic and photovoltaic applications. Using density functional theory (DFT) with GGA-PBE and mGGA-rSCAN functionals, we analyzed the structural, electronic, optical, mechanical, phonon, population, and thermoelectric properties of these compounds. All Z3BrO materials exhibit direct band gaps and strong optical absorption in the visible-UV spectrum. Mechanical and phonon analyses confirm their dynamic and elastic stability, with K3BrO showing superior mechanical robustness and Fr3BrO demonstrating the highest Debye temperature. SCAPS-1D simulations were conducted on heterostructures incorporating K3BrO, Rb3BrO, and Cs3BrO as absorber layers. The results revealed PCEs of 23.26% for K3BrO, 25.58% for Rb3BrO, and 26.43% for Cs3BrO, highlighting the tunability and performance potential of these materials. Fr3BrO, while excluded from device simulation due to its near-metallic nature, exhibited promising optical and thermal features. These findings establish Z3BrO anti-perovskites as promising, lead-free absorber materials for high-performance and sustainable solar energy technologies.