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

Abstract

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.