Electronic, optical, and photovoltaic properties of the NaBiS2 compound with orthorhombic structure: A highly perspective photoferroic material

Density Functional Theory (DFT) calculations were conducted to explore the electronic, optical, and photovoltaic properties of the NaBiS2 compound with orthorhombic structure, aiming to evaluate its potential for ferroelectric-photovoltaic applications in solar cells. Exchange and correlation electronic effects were approximated using Tran and Blaha's modified Becke-Johnson potential in its semiconductor variance form. The compound was found to have a direct band gap of 1.2 eV, with an absorption coefficient exceeding 105 cm−1 for photon energies higher than 2.2 eV. The material exhibits a pronounced optical anisotropy. Optical absorption in the visible range is primarily caused by electron transitions from the S 2px,y to the Bi 2px,y states. Photoconversion efficiency (PHCE) under sunlight reaches a maximum of 20% for a film thickness of approximately 5 μm. This efficiency surpasses that of the MAPbI3 perovskite compound, a ferroelectric-photovoltaic material with the highest experimental power conversion efficiency (PCE) to date, by 4%. These findings, combined with previously published estimates of ferroelectric polarization and the mobility of charge carriers, uncover the unexplored potential of the orthorhombic NaBiS2 compound to be employed in photovoltaic and solar-cell devices.