The Research Of The Positive/negative Photoconductivity Effect In CsPbBr₃ Nanocrystals/graphene Heterostructure

Nowadays,mobile phone screens automatically change brightness according to the environment,security inspection equipments use infrared radiation to detect objects,various types of spectrometers help us study the properties of materials.As an important part of these equipment,photoelectric sensor elements have extremely wide applications in life,safety,industry and study fields.Electronic equipment is developing towards miniaturization and functional integration,and so do photoelectric sensor elements.Making broadband response photodetector is an important way to realize the functional integration of photoelectric sensor components.The broadband photodetector is a device that has a wide wavelength response range and can even generate photoelectric response to light of multiple bands.This kind of device can effectively simplify the circuit design.Most of the broadband photodetectors that have been reported so far work based on the conventional internal photoelectric effect of semiconductor materials,such as Positive photoconductivity(PPC)effect,Photovoltaic effect and Grating effect,etc.Under the irradiation of a specific wavelength of light,device generates a positive photocurrent.However,in actual detection,the optical power density and incident angle of the incident light is uncertain.Therefore,the broadband photodetector cannot accurately distinguish the wavelength of the incident light by comparing the value of photocurrent,which affects its practical application prospects in the future.Negative photoconductivity(NPC)effect refers to the special photoelectric effect that the conductivity of material decreases under irradiation,and this effect can generate a negative photocurrent.If the broadband photodetector can generate a positive photocurrent and a negative photocurrent to the light of the different wavelength respectively,it can accurately distinguish the wavelength of the incident light according to the direction of the photocurrent,and this can greatly improve the optical recognition accuracy of the broadband photodetector.Therefore,it is very beneficial to the development of broadband photodetectors to make devices capable of generating positive photoconductivity(PPC)responses and NPC responses to light of different wavelengths,respectively.In view of this demand,the research works of this paper are as follows:Firstly,Cs Pb Br₃nanocrystals(NCs)and multilayered graphene were synthesized by thermal injection and chemical vapor deposition methods,and then Cs Pb Br₃NCs were spin-coated onto graphene to form a Cs Pb Br₃NCs/graphene heterojunction;Many methods are used to characterize the related characteristics of Cs Pb Br₃nanocrystals film,graphene film and Cs Pb Br₃NCs/graphene heterojunction.Secondly,the I-t response of Cs Pb Br₃NCs/graphene heterojunction under irradiation were measured.This device generated PPC response at 420?510 nm,and generated NPC response at 300?390 nm.Afterwards,through the analysis of the heterojunction band structure and the characteristics of graphene,the generating reasons of PPC and NPC effect are summarized:(1)Under the irradiation of visible-light(420?510 nm),the photogenerated carrier behavior of Cs Pb Br₃NCs increases the carrier concentration of graphene,increasing the conductance of the graphene(PPC).(2)Under the irradiation of UV(300?390 nm)laser,photothermal effect leads to the violent lattice vibration,then the water molecules adsorbed on the graphene surface are desorbed.The P_z-orbital electrons bound by the water molecules return to the graphene's valence band,decreasing the hole concentration and conductance of the graphene(NPC).Finally,the application prospect of Cs Pb Br₃NCs/graphene heterojunction in the field of ultraviolet-visible light broadband photodetection is introduced,and the influence of Cs Pb Br₃NCs film thickness,graphene film thickness and device substrate thermal conductivity to the PPC and NPC effect in this heterojunction are investigated.