Low-Symmetry 2D Ta2PtSe7 Induced by Ultralong Structural Motifs for Flexible Long-Wave Infrared Photodetection up to 10.6 µm.

The limited ability of traditional 2D anisotropic materials to meet next-generation anisotropic device demands necessitates innovative design strategies. To address this challenge, a symmetry-reduction approach is proposed that enhances in-plane anisotropy by extending structural motifs to lower crystal symmetry. Implementing this design principle, a novel van der Waals material, Ta2PtSe7 atomic layers is successfully developed, featuring record-breaking [Ta4Pt2Se14] structural motifs with an unprecedented length of 20.1 Å. This unique architecture endows Ta2PtSe7 with remarkable intrinsic in-plane anisotropy, manifesting in strongly direction-dependent optical and electrical characteristics. The developed Ta2PtSe7-based photodetector demonstrates exceptional broadband responsiveness across an expansive spectral range from visible to long-wavelength infrared (LWIR; 671 nm-10.6 µm). Particularly noteworthy is its outstanding performance under low operating voltage (0.1 V), achieving a high responsivity of 27 V W-1 at 10.6 µm illumination - a significant advancement in LWIR detection capabilities. Furthermore, flexible device configurations exhibit excellent mechanical robustness, maintaining over 70% of initial photocurrent after 50 bending cycles, demonstrating promising potential for flexible optoelectronics. This study proposes a novel structural motif engineering strategy to design anisotropic materials, exemplified by Ta2PtSe7's exceptional in-plane anisotropy, broadband photoresponse, and mechanical robustness, enabling high-performance anisotropic optoelectronic devices.