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

Abstract

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.