▎ 摘　　要

The exploration of various two-dimensional (2D) materials provides a promising platform for constructing van der Waals heterojunction (vdWH) photovoltaic devices. The photovoltaic efficiency of such devices is still a challenge due to the recombination of photogenerated carriers resulting from the intrinsic doping property of materials. Here, PdSe2-based graphene-sandwiched vertical devices with high photovoltaic efficiency are constructed. As the graphene-sandwiched structure limits the diffusion length to tens of nanometers, the carrier recombination during diffusion is spontaneously reduced. Moreover, due to the low-resistance contact of graphene/PdSe2, the Fermi level and carrier density of PdSe2 can still be significantly tuned by gate voltage, which leads to a sharp enhancement of built-in field and photovoltaic effect. As a result, the Gr/PdSe2/MoS2/Gr vdWH photovoltaic device shows a high power conversion efficiency of 3.9% and an open circuit voltage of 0.6 V under 650 nm laser illumination at room temperature. The present work provides an efficient scheme for the design of high-efficiency 2D material photovoltaic devices.