Spin-dependent photovoltaic effect and anisotropic light absorption in the two-dimensional magnetic semiconductor MnNF

The development of van der Waals magnetic semiconductors has created a fascinating platform for exploring spin-dependent optoelectronic properties in the two-dimensional (2D) limit. However, the light absorbance in most 2D ferromagnetic (FM) semiconductors is extremely low, which strictly restricts the generation efficiency of spin-polarized currents. Using first-principles calculations and group theory analysis, we demonstrate that the light absorbance of FM monolayer MnNF exhibits pronounced anisotropy in light absorbance for light polarized along the $x$ and $y$ directions. Specifically, the lowest-energy optical absorption peaks are significantly higher than those of well-studied FM semiconductors such as monolayer ${\mathrm{CrI}}_{3}$ and CrSBr. The high absorbance primarily originates from transitions between the N-$p$ and Mn-$d$ orbitals, which can be explained using the group theory analysis. Notably, the photogenerated electrons and holes are fully spin polarized in the visible range, with absorbed photon flux comparable to that of the reported high-performance ultrathin solar cells using transition metal dichalcogenides. Furthermore, the direct absorption edge is dipole forbidden, indicating a long carrier recombination lifetime. Additionally, we show that the light absorbance can be effectively tuned by both strain and thickness. These findings highlight MnNF as a promising candidate for next-generation optospintronic devices.