Manipulation Of Photoluminescence Of 2D Transition Metal Dichalcogenides

Compared with conventional semiconductors and graphene,2D Transition metal dichalcogenides（2D TMDCs）have ultra-thin thickness,good flexibility,significant valley electronics features,direct band gap covering visible and near infrared range and many other properties.As a direct bandgap material,2D TMDCs show practical prospects in the fields of photoelectric detector,optical switch and LED.However,their poor light absorption rate caused by the ultra-thin thickness,vulnerability to the ambient by the high surface-tovolume ratio,as well as their inherent low quantum yields restricts severly their application.Therefore,it is necessary to optimize the photoelectric characteristics of the 2D TMDCs.Based on these situation,we carried out a series of studies on the control of photoluminescence（PL）of 2D TMDCs,and some good results have been obtained.The main contents of this paper are as follows:（1）We found a strong PL degeneration in the 3-month aged monolayer（ML）WS₂:PL intensity weakening,spectral broadening to the long wavelength range and a red shift of the PL peak.Through the analysis of PL spectra,we found that PL degradation could be attributed to the emergence and enhancement of PL spectra from charged excitons in ML WS₂.Based on this,we proposed firstly the method of using PC₆₁BM to modify the ML WS₂,and proved the feasibility of this method by experiment.After modification,the formation of the charged exciton in ML WS₂ was greatly inhibited,and its PL peak is kept near the exciton.The broadening of the spectrum is reduced and the PL distribution of ML WS₂ is much more uniform.（2）In heterostructures with different band alignmen,the different transmission direction of electron and hole will have a different impact on the properties of materials.Based on this viewpoint,we have chosen two different materials to manipulate the PL of ML WS₂.Perovskite quantum dots CsPbBr₃ can form a type I heterostructure with ML WS₂,where ML WS₂ is the narrower band gap materials.Thus the photo-induced electrons and holes intended to transfer into the conduction band and valence band of ML WS₂,improving the excitons concentration in ML WS₂,raising its PL quantum yield by 4 times and increasing its PL intensity by nearly 13 times.The related work was praised as the Spotlight by the OSA（American optical society）.On the other hand,the quantum dots FAPbBr₃ and ML WS₂ can form type II heterostructure,which causes the electrons and holes to be separated and transferred to different materials,resulting in PL quenching of both.It can be seen that the energy band structure of the materials is an important index for the effective manipulation over the optical properties of the 2D TMDCs.（3）Study on the manipulation over the optical properties of 2D TMDCs by electric field is very beneficial for designing better optoelectronic devices based on 2D TMDCs.We made a ML MoS₂ field-effect transistor,and explored its PL behavior under different gate voltage and source drain voltage at room temperature.It is found that negative gate voltage can effectively improve the PL intensity of the ML MoS₂,while the positive gate voltage has an opposite influence.The existence of source drain voltage weakened the PL intensity definitely.