Large ferroelectric photovoltaic effect of a wurtzite-structure SnC/ScN superlattice

Abstract

A high bandgap is the most important factor impeding the development of ferroelectric photovoltaic (FE-PV) materials. Finding a new FE-PV material with a narrow bandgap is thus very urgent. Here, a wurtzite-structure SnC/ScN (w-SSCN) superlattice was constructed to obtain light absorption properties using first-principles calculations based on the narrow bandgap of group IV and their alloys. The mechanic and dynamic calculations show that w-SSCN is stable. It has a lower band gap (2.796 eV) and a larger visible absorption coefficient than traditional ferroelectric material BaTiO3, and is even close to Si. In addition, ferroelectric polarization switching can be achieved due to the small barrier (0.215 eV). The polarization decreases under tensile strain, but the visible light absorption is enhanced due to the decrease in the bandgap. Meanwhile, the switching barrier reduces. The w-SSCN with 4% tensile strain exhibits a remarkable visible light absorption property due to the narrow bandgap (1.216 eV), and its spontaneous polarization is relatively large (0.535 C/cm2) under a low switching barrier (0.011 eV). The density of states diagram shows that the conduction band minimum (CBM) state and the valence band maximum (VBM) state come from the Sn 5 s and C 2p states, respectively. The contributions of electrons and holes originating from the different atoms suppress recombination, which enhances the solar power conversion efficiency. This work provides a new way to promote the development of FE-PV materials.