DFT-based investigation of thermal, dynamic, mechanical, optoelectronic, and strain-engineered properties of a novel lead-free Na3SeBr inorganic anti-perovskite compound and achieving over 29 % photovoltaic efficiency

Inorganic anti-perovskite materials have recently attracted attention as lead-free, non-toxic, structurally stable, and cost-effective optoelectronic components. In this study, the structural, electronic, optical, thermal, phonon, and mechanical properties of the new Na 3 SeBr anti-perovskite compound were investigated using first-principles (DFT-GGA-PBE) methods, with tensile and compressive strains up to ±6% applied. The optimized (unstrained) compound exhibits a direct bandgap of 2.3653 eV at the Γ-point, suitable for visible light. Bandgap tuning under strain shows 2.63 eV at −6%, 2.52 eV at −4%, 2.43 eV at −2%, 2.36 eV at 0%, 2.27 eV at +2%, 2.18 eV at +4%, and 2.10 eV at +6%, demonstrating the controllability of its optoelectronic properties. Phonon calculations reveal dynamic stability at all strains except a slight instability at −6%. Mechanical analysis shows that the elastic constants satisfy Born stability criteria under all strains. The B/G ratio varies between 1.72 and 1.88, indicating inherent ductility, which increases under both tensile strain and compressive strain. Low bulk and Young’s moduli reflect the soft nature of Na 3 SeBr, suitable for flexible thin-film devices. Optical analysis indicates high absorption (~0.8×10 5 –14×10 5 cm -1 ) in the visible-UV range, along with favorable reflectance and dielectric properties, ensuring efficient light harvesting and electron-hole generation. The work function in the unstrained state is 3.4316 eV, supporting effective electron emission. A novel Al/FTO/WS 2 /Na 3 SeBr/Cu 2 O/Se solar cell was designed and simulated using SCAPS-1D. Optimization of the absorber thickness, defect density, and shallow acceptor density at 300 K yielded a PCE of 29.135%, a J sc of 23.04 mA/cm², a V o of 1.468 V, and a fill factor of 86.08%, outperforming many existing lead-free and lead-based perovskite solar cells. Overall, Na 3 SeBr is an environmentally friendly, cost-effective, and high-performance anti-perovskite material. Its strain-tunable bandgap, strong optical absorption, and mechanical flexibility make it a highly promising candidate for next-generation solar cells, optoelectronic devices, and thermoelectric applications. • DFT and SCAPS-1D based investigation of novel Na 3 SeBr inorganic anti-perovskite. • The proposed novel Na 3 SeBr anti-perovskite is structurally, thermally, dynamically, and mechanically stable. • Na 3 SeBr is a direct bandgap semiconductor, with a band gap of 2.3653 eV at the Γ-point, and has high optical absorption in the UV to visible wavelength range. • Na 3 SeBr inorganic anti-perovskite has been shown to be suitable for applications in photodetectors, UV protection and radiation detection, and optical and photovoltaic devices. • The proposed anti-perovskite solar cell (APSC) Al/FTO/WS 2 /Na 3 SeBr/Cu 2 O/Se structure was designed and optimized in SCAPS-1D simulator. • The recommended APSC demonstrates promising efficiencies of a maximum of 29.135%, highlighting their potential for high-performance photovoltaic applications of Na 3 SeBr compound.