Performance Analysis Of WS₂-rGO Hybrid Photodetector

Since graphene was first discovered in 2004,this unique two-dimensional（2D）nanomaterial has been widely studied in the past ten years.Disappointingly,the low Ion/Ioff ratio and low photoresponsivity greatly limit the application of this star material in the field of photodetectors.Meanwhile,the atomically thin tungsten disulfide（WS₂）,an emerging 2D material,exhibits an extraordinary I_on/I_off ratio and high absorption coefficient,making it more practical application prospects in photodetector devices.But WS₂ has a fatal disadvantage of high carrier recombination.In the past few years,transition metal dichalcogenide（TMD）/graphene heterostructures have enhanced photodetection performance compared to pure TMD due to the high carrier mobility of graphene.Therefore,constructing a heterostructure of graphene and WS₂ can compensate for the shortcomings of high carrier recombination ratio of WS2.Although some researches based on WS2/graphene photodetectors have been reported,their preparation processes are complicated,time consuming and uneconomical.Most importantly,these photodetectors need to be driven by an external power source.In this case,constructing self-powered photodetectors is of great significance for sustainable development.In this paper,single-layer WS₂ nanosheets were prepared by lithium ion intercalation exfoliaton method.On this basis,WS2-reduced graphene oxide（WS2-rGO）hybrids were synthesized by one-step hydrothermal method.Their self-powered photoelectric properties were studied by conventional photoelectrochemical systems（PEC）.The detailed research contents are as follows:First,the WS2 nanosheets were successfully exfoliated by lithium ion intercalation exfoliation and the microscopic morphology and structure of as-prepared samples were characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD）and Raman.The results show that WS₂ has a fast and stable photoresponse capability at zero bias,as well as the photocurrent of the WS₂nanosheets reaches to 70.4 nA/cm² at a bias voltage of 0.8V.In addition,the photocurrent of WS₂ improves while its photocurrent increment decreases as the bias voltage increases.This is due to the fact that the bias creates a potential potential gradient in the WS₂ nanosheet that promotes the separation of photogenerated carriers and reduces their recombination rate.As a result,the photocurrent increases as the potential increases until most of the photogenerated electrons react with the electron scavenger on the surface of the photoelectrode or transfer to the cathode under the influence of the electric field.Second,the WS2-rGO hybrids were synthesized by one-step hydrothermal method.The microscopic morphology and structure of the hybrids were characterized by SEM,XRD and Raman techniques.The photoelectric properties of WS₂-rGO hybrids were tested by PEC system.It was found that WS₂-rGO hybrid has a higher photocurrent than the pure WS2 nanosheets,indicating that the introduction of graphene is beneficial to increase the photoresponse performance.The photocurrent density of the WS2-rGO hybrid at 0.8V is twice that at zero bias,indicating that the bias potential can effectively modulate its photocurrent.Since the WS₂-rGO photodetector still has an effective photoresponsive performance without an external power source,it can be a promising photoelectrode of self-powered photodetectors.In addition,the photocurrent of the WS2-rGO photodetector is approximately linear with the light power intensity.Its photoresponsvity reaches up to 9.3μA/W at an illumination intensity of 30 mW/cm².