First-principles investigation of the structural, electronic, and optical properties of a novel Na3SI anti-perovskite for efficient solar-to-hydrogen energy conversion via photocatalytic water splitting

In this research, a new Na 3 SI anti-perovskite design and its structural, mechanical, dynamical, and optoelectronic features have been theoretically analyzed using density functional theory (DFT)-based methods with GGA-PBE functionalization in Quantum ESPRESSO software. The optimized structure, phonon dispersion, and elastic constant analysis show that the material is dynamically and mechanically stable. The Na 3 SI has a direct bandgap of 2.499 eV at the gamma point, which is suitable for water splitting. Also, the Na 3 SI exhibits strong absorption of 0.5 × 10 5 cm −1 (visible region) and 13 × 10 5 cm −1 (UV region). Furthermore, the alignment of its conduction and valence band edges with the redox potential of water splitting suggests its capability to generate hydrogen and oxygen under visible light. Next, this study designed an Al/Na 3 SI/Se structure that provides 25.769 % solar-to-hydrogen energy conversion efficiency. The research highlights Na 3 SI as a promising candidate not only for photocatalytic water splitting but also for photovoltaic and optoelectronic technology.