Intrinsically anisotropic van der Waals crystals for broadband polarization‐sensitive photosensing

Polarization‐resolved photosensor is crucial in imaging and communication technologies. Molybdenum trichloride (MoCl 3 ), as a typical two‐dimensional (2D) transition metal trihalide, features the largest distortion in the transition metal‐based honeycomb skeletons, giving rise to the intrinsic in‐plane anisotropy that is ideal for polarization‐resolved optoelectronic devices. Here, we report the synthesis of MoCl 3 van der Waals crystals using a solid‐phase reaction method for the application of a polarization‐sensitive photodetector. The as‐synthesized MoCl 3 demonstrates high single crystallinity, which is validated by collaborating with X‐ray diffraction, transmission electron microscopy, and Raman characterizations. Additionally, the intrinsic lattice anisotropy of MoCl 3 is illustrated by probing the orientation‐specific phonon vibration modes using polarized Raman and second‐harmonic generation spectra. By leveraging the extraordinary anisotropic characteristic, we fabricated MoCl 3 photosensors for the detection of polarized optical signals, with a high linear dichroic ratio of 4.2 at 532 nm and fast photoresponse speed (<2 ms) from visible to near‐infrared bands. Moreover, the device demonstrates outstanding ambient stability, as revealed by its retained photoresponse behavior after being exposed to air for 6 months. Our results demonstrate the advantages of highly anisotropic crystals in hosting polarization‐sensitive photosensing functions, opening up new possibilities in developing innovative optoelectronic units.