Self‐Powered Polarization‐Sensitive Near‐Infrared Photodetection Based on 2D Bi 4 O 4 SeCl 2

Self‐powered polarization‐sensitive photodetection is crucial for next‐generation low‐power optoelectronic systems. Yet, the development of such devices has been hindered by the scarcity of suitable materials combining intrinsic in‐plane anisotropy with efficient zero‐bias photoresponse. Here, we report the first comprehensive investigation of the in‐plane anisotropic properties of Bi 4 O 4 SeCl 2 , a van der Waals material exhibiting pronounced 2D anisotropy that has remained unexplored until now. Through physical vapor transport growth, we obtained high‐quality Bi 4 O 4 SeCl 2 single crystals featuring a quasi‐tetragonal layered structure with strong in‐plane electronic and optical anisotropy. Photodetectors fabricated from mechanically exfoliated Bi 4 O 4 SeCl 2 flakes exhibit broadband responsivity from the visible to near‐infrared range (532–1064 nm), self‐powered operation at zero bias, and rapid response times (∼0.47/0.49 s). Spatially resolved scanning photocurrent microscopy and photovoltage mapping confirm that the dominant photoresponse arises from the photothermoelectric effect. Notably, the device exhibits exceptional polarization sensitivity, achieving polarization ratios of 1.93 and 1.76 at wavelengths of 671 and 1064 nm, surpassing the performance of most previously reported zero‐bias near‐infrared photodetectors. Angle‐resolved polarized Raman spectroscopy reveals a distinct fourfold rotational symmetry, further confirming the strong in‐plane anisotropy. These findings establish Bi 4 O 4 SeCl 2 as a multifunctional layered material with significant potential for next‐generation, low‐power, polarization‐resolved photodetectors.