Photoelectric Properties Of Bi₂X₃（X=S,Se,Te） And Their Heterostructures

Two-dimensional narrow-bandgap semiconductor materials show abundant edge active sites,wide spectral absorption range（covering the ultraviolet-near-infrared light band）,and high carrier mobility.As a new generation of optoelectronic functional materials,these materials have great applications in optoelectronic devices,such as photodetectors,solar cells,and photoelectric catalytic electrodes.Bi₂Se₃ and Bi₂Te₃ are typical narrow-bandgap semiconductors（0.3-1.0 eV）with strong light-matter interactions and high conductivity as well as high specific surface areas.Furthermore,Bi₂Se₃ and Bi₂Te₃ are also typical topological insulators.The surface is fermions determined by the Dirac equation with spin-momentum locking,and the body is an insulator with a bandgap.However,the photoelectric properties of single 2D narrow-band gap Bi₂Se₃ and Bi₂Te₃ are greatly limited due to the rapid recombination of electron-hole pairs.Therefore,how to improve the performance of optoelectronic devices based on these two-dimensional materials is an urgent issue to be solved.This paper focuses on the process of electron-hole pair separation and transport at the interface,and solves these issues of slow carrier separation and transfer rate and high recombination rate by constructing a heterostructure.The formation of heterostructure not only achieves high-response and high-sensitivity photodetection in photodetector and improves the photocatalytic hydrogen production.The main research contents and innovative achievements are as follows:（1）Preparation of SnS₂/Bi₂X₃（X=Se,Te）heterostructures and their photodetection performanceConstructing different type heterostructures can modulate the interfacial charge transportation.In this section,SnS₂/Bi₂X₃（X=Se,Te）van der Waals heterostructures were fabricated by physical vapor deposition（PVD）and chemical vapor deposition（CVD）.Combined with UV-Vis spectroscopy and photoelectron spectroscopy analysis,it is confirmed that SnS₂/Bi₂Se₃ belongs to type-Ⅰ band arrangement,and SnS₂/Bi₂Te₃ belongs to type-Ⅱ band arrangement.The photoelectric response of the photoelectrochemical（PEC）-type photodetector is characterized based on the traditional three electrode system.The results show that the photocurrent densities of both type-Ⅰ SnS₂/Bi₂X₃ and type-Ⅱ SnS₂/Bi₂Te₃ heterostructures are an order of magnitude larger than those of SnS₂,Bi₂Se_3,and Bi₂Te₃.This improvement is mainly from the enhanced light absorption and efficient carrier separation at the heterostructure interface.Based on the construction of type-Ⅰ and type-Ⅱ heterostructures,this work provides a new pathway for developing high-performance photodetectors and other optoelectronic devices.This part of the work has been published in Science China-Materials.（2）Preparation of Bi₂Te₃/Bi₂Se₃/Bi₂S₃ cascade heterostructure and study of its photodetection performanceTwo-dimensional heterostructures have been widely used in optoelectronic devices such as photodetection and photocatalysis.However,simple double-layer heterostructures is limited to improve the performance of optoelectronic devices.Therefore,seeking for high performance of novel photodetectors has important research significance.In this section,Bi₂Te₃/Bi₂Se₃/Bi₂S₃ van der Waals cascade heterostructure was synthesized by CVD and PVD methods.The band alignment of Bi₂Te₃/Bi₂Se₃/Bi₂S₃ cascade heterostructures was measured by UV-Vis spectroscopy and photoelectron spectroscopy.The results show the photocurrent density of the Bi₂Te₃/Bi₂Se₃/Bi₂S₃ cascade heterostructure reaches 2.2 mA/cm²,which is approximately 169 times larger than that of Bi₂Te₃,approximately 122 times larger than that of Bi₂Se₃,and approximately 18 times that of Bi₂S₃.Compared with the Bi₂X₃/Bi₂X₃（X=S,Te,Se）heterostructure,the photoelectric response of the Bi₂Te₃/Bi₂Se₃/Bi₂S₃ cascade heterostructure is also greatly improved.The photocurrent density of Bi₂Te₃/Bi₂Se₃/Bi₂S₃ cascade heterostructure is approximately 8.5 times larger than that of the Bi₂Te₃/Bi₂Se₃ heterostructure.This value is approximately 2.2 times larger than that of Bi₂Se₃/Bi₂S₃ heterostructure and approximately1.4 times that of Bi₂Te₃/Bi₂S₃ heterostructure.This work provides new ideas and methods for developing high-performance photodetectors and other optoelectronic devices based on three-layer van der Waals heterostructures.（3）Study on Bi₂X₃（X=S,Te,Se）and their heterostructures in photoelectrocatalytic hydrogen productionBased on the photodetection performance of Bi₂Te₃/Bi₂Se₃/Bi₂S₃ cascade heterostructure,it has been demonstrated that the construction of three-layer van der Waals heterostructure can greatly improve the photoelectric conversion efficiency.Herein,we also explore the photoelectrocatalytic hydrogen production based on the Bi₂Te₃/Bi₂Se₃/Bi₂S₃ cascade heterostructure.The efficiency of photoelectrocatalytic hydrogen production is limited by many factors.The photoelectric catalytic hydrogen production was measured under different wavelengths,different external bias voltages,and with or without sacrificial agents.The results show the Bi₂Te₃/Bi₂Se₃/Bi₂S₃ cascade heterostructure exhibits strong photoelectrocatalytic performance,and the production of hydrogen can stably generate 1.25 mmol/cm² within 3 hours.Compared with Bi₂X₃（X=S,Se,Te）and Bi₂X₃/Bi₂X₃（X=S,Te,Se）heterostructures,the efficiency of photoelectrocatalytic hydrogen production was also greatly improved.Furthermore,we also investigate the photocatalytic hydrogen production,electrocatalytic hydrogen production,and photoelectrocatalytic hydrogen production of Bi₂Te₃/Bi₂Se₃/Bi₂S₃ cascade heterostructures.The results show that the input light and external applied voltage have a synergistic effect on the improvement of catalytic hydrogen production performance.This work provides an idea and a theoretical reference for improving the photocatalytic performance by constructing a cascade heterostructure.