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

Van der Waals (vdW) heterojunction has emerged as promising building blocks for the next generation of optoelectronics, which can fulfill the increasing demands of miniaturization, high density of integration, and low power consumption. The photovoltaic effect is one of the crucial functions for fast photo-detection and energy-harvesting applications. Here, graphene is integrated into vdW WS2/WSe2 heterojunction, the graphene can serve as electron and hole transport layers, boosting the collection efficiency of photo-excited carriers and thus improving the photovoltaic effect. The graphene-integrated device exhibits superior power-conversion-efficiency (PCE) up to 9.08%, one order of magnitude improvement compared to the device with metal-WS2/WSe2-metal configuration. Moreover, the back gate has great modulation on its photovoltaic effect due to the large gate-tunability of band bending at the interface. Operating as self-driven photo-diode, it also achieves outstanding photodetection performance with high photo-switching ratio of 1 x 10(6), high detectivity (D*) of 2.66 x 10(12) Jones, and fast speed of 110 mu s, all the parameters are improved by nearly one order of magnitude compared to the device without graphene integration. This work provides a universal approach by integrating graphene as vdW contact to significantly improve the photovoltaic effect and photodetection property toward highly efficient energy-harvest and photodetector applications.