MXene V₂CT_x Nanosheet/Bismuth Quantum Dot-Based Heterostructures for Enhanced Flexible Photodetection and Nonlinear Photonics

Recently, novel two-dimensional materials, e.g., Xenes (graphdiyne, phosphorene, bismuthene, antimonene, etc.) and MXenes, have drawn great attention in nanophotonics due to their excellent flexibility, high photothermal conversion efficiency, and large thermal conductivity. Although the Xenes and MXenes have achieved rapid progress in many fields over the past decade, their relatively poor photodetection and nonlinear photonics have still limited their practical applications. In this work, a mixed-dimensional 2D MXene V 2 CT x nanosheet (NS)/0D bismuth quantum dot (Bi QD)-based heterostructure fabricated by a combination of selective etching and the hydrothermal method was simply deposited onto a clean poly(ethylene terephthalate) substrate with an embedded regular Ag lattice to prepare a flexible photoelectrochemical (PEC) electrode. The PEC result shows that the as-fabricated flexible electrode not only exhibits significantly improved photocurrent density (32.7 μA cm –2 ) and photoresponsivity (906 μA W –1 ) compared to individual MXene V 2 CT x NSs and Bi QDs but also displays high stability with a stable photocurrent density even after 200 bending cycles at 60°. Taking advantage of the Kerr effect of both MXene V 2 CT x NSs and Bi QDs, an all-optical switcher based on this mix-dimensional heterostructure for the spatial cross-phase modulation has also been realized with a preferred modulation depth. Density functional theory calculations provide direct evidence for the strong internal built-in electric field (7.3 × 10 7 eV m –1 ) created by the heterostructure for the enhancement of both photodetection and nonlinear photonics. The integration of Xenes or MXene-based mixed-dimensional heterostructures provides a concept and fundamental guidance to construct next-generation optoelectronic and photonic devices.