Integrating Graphene Enables Improved and Gate-Tunable Photovoltaic Effect in Van der Waals Heterojunction

摘要

Van der Waals (vdW) heterojunction has emerged as promising buildingblocks for the next generation of optoelectronics, which can fulfill theincreasing demands of miniaturization, high density of integration, and lowpower consumption. The photovoltaic effect is one of the crucial functionsfor fast photo-detection and energy-harvesting applications. Here, grapheneis integrated into vdW WS_2/WSe_2 heterojunction, the graphene can serveas electron and hole transport layers, boosting the collection efficiencyof photo-excited carriers and thus improving the photovoltaic effect. Thegraphene-integrated device exhibits superior power-conversion-efficiency(PCE) up to 9.08%, one order of magnitude improvement compared to thedevice with metal-WS_2/WSe_2-metal configuration. Moreover, the back gatehas great modulation on its photovoltaic effect due to the large gate-tunabilityof band bending at the interface. Operating as self-driven photo-diode, it alsoachieves outstanding photodetection performance with high photo-switchingratio of 1 × 10~6, high detectivity (D*) of 2.66 × 10~(12) Jones, and fast speed of110 μs, all the parameters are improved by nearly one order of magnitudecompared to the device without graphene integration. This work provides auniversal approach by integrating graphene as vdW contact to significantlyimprove the photovoltaic effect and photodetection property toward highlyefficient energy-harvest and photodetector applications.