Strain tunable high absorptivity and carrier mobility in two-dimensional multiferroic Cr2SOCl2 monolayer

Based on first-principles calculations, this paper presents a study on the stability, electronic structure, ferromagnetic, ferroelectric, and optical properties of Cr2SOCl2 monolayer. The calculations reveal that the Cr2SOCl2 monolayer is a typical magnetoelectric and bipolar magnetic semiconductor with a direct bandgap of 1.25 eV, where the ferromagnetic and ferroelectric ordering can coexist simultaneously below 76 K. The electronegativity difference between S and O atoms leads to a redistribution of charge, which drives the ferroelectric polarization of the Cr2SOCl2 monolayer. The application of uniaxial strain allows for the control of bandgap, light absorption, and carrier mobility in Cr2SOCl2 monolayer. Specifically, when a tensile strain is applied along the y direction, the monolayer undergoes a transition from the bipolar magnetic semiconductor to ferromagnetic half-semiconductor phase. At 12% strain, the absorptivity of Cr2SOCl2 monolayer can reach the maximum (∼8%) within the visible light range; moreover, the mobility of both electrons and holes is large in the x direction, but their difference is small, almost on the same order of magnitude. Based on these findings, we propose that Cr2SOCl2 monolayer under this strain could be a promising ferroelectric photovoltaic material for the absorption layer in solar cells.