Giant structure anisotropy and highly polarization-sensitive photodetection in quasi-1D van der Waals Nb₄P₂S₂₁

High performance polarization sensitive photodetectors have attracted significant attention in optoelectronics. Low-dimensional semiconductors with asymmetric crystal lattices are ideal polarization detection media due to their inherent optical and electronic anisotropies. Among them, the emerging quasi-one-dimensional van der Waals metal phosphorus sulfide, Nb4P2S21, exhibits prominent in-plane optical anisotropy and broad UV-visible light absorption. To validate its application potential for polarization-sensitive photodetection, herein, the anisotropic lattice vibrational and optical characteristics of Nb4P2S21 were systemically investigated by angle-resolved polarized Raman, transmission and reflection spectroscopies. Leveraging these properties, we fabricate a planar two-terminal Nb4P2S21-based photodetector, which demonstrates a stable broadband photoresponse and pronounced polarization sensitivity, delivering a responsivity of 0.29 mA W⁻¹ and a high anisotropic ratio of 2.53 at 405 nm. Beyond revealing fundamental correlations between crystal symmetry and optical response, these findings establish Nb4P2S21 as a promising candidate for next-generation polarization-sensitive optoelectronic devices.