Two-dimensional Janus NbOClI: A promising anisotropic unit for multifunctional optoelectronic devices
Degao Xu, Luyang Lv, Meng Ge, Jiansheng Dong, Shanjun Chen, Chenjie Dai, Xianzhuo Wang, Jiahua Xu, Jianing Tan, Wen‐Xing Yang, Gang Ouyang
Abstract
Recently, the synthesis of a ${\mathrm{NbOCl}}_{2}$ monolayer has been reported, revealing notable anisotropic properties and linear dichroism [Guo et al., Nature (London) 613, 53 (2023)]. Inspired by this progress, we have engineered a Janus NbOClI monolayer by breaking the out-of-plane spatial inversion symmetry in ${\mathrm{NbOCl}}_{2}$. Through rigorous first-principles calculations, we present a detailed and comprehensive investigation of its mechanical and optical characteristics. We find that it exhibits a substantial out-of-plane piezoelectric response (${d}_{31}=0.87$ pm/V), driven by atomic electronegativity differences and Peierls distortion. The intrinsic electric field within NbOClI enables robust photocatalytic water-splitting capabilities across a broad pH spectrum, independent of external strain. Capitalizing on its pronounced linear dichroism, we construct a polarization-sensitive photodetector that leverages the photogalvanic effect to produce an anisotropic, self-powered photocurrent. Notably, this photocurrent is significantly amplified by a strain gradient, achieving self-rectification via the synergistic coupling of flexoelectric and piezoelectric fields. Building upon these achievements, a proof-of-concept three-channel optical communication scheme is shown to amplify the output efficiency of binary signals by an additional $50%$. Our results present a fascinating functional coupling architecture that simultaneously enables excellent force-electric conversion, efficient photocatalytic water splitting, polarization-sensitive self-powered photodetection, and multichannel optical communication in Janus NbOClI-based optoelectronic devices. This brings us closer to realizing the next generation of chip-scale integrated optoelectronics.