Self-powered photodetectors based on stacked WSe2/graphene/SnS2 p-g-n heterostructures

The insertion of a graphene interlayer between van der Waals (vdW) materials could suppress the interlayer recombination to improve interface quality and facilitate charge transport. However, its effect on photovoltaic-mode detectors has rarely been explored. Here, self-powered photodetectors based on WSe2/graphene/SnS2 vdW heterojunctions were assembled and the impact of adding graphene interlayer on its performance was investigated. The p-g-n heterostructure exhibits a photovoltaic characteristic, VOC = 0.13 V and ISC = 0.12 nA under illumination of 2.98 mW/cm2@405 nm, lower than that of a control (WSe2/SnS2) counterpart (VOC = 0.19 V and ISC = 1.15 nA). Yet an FF value up to 48.16 % was obtained under an irradiation power density of 0.332 mW/cm2@405 nm, which is visibly higher than that of bare WSe2/SnS2 vdW heterostructure. The insertion of graphene interlayer is deemed to reduce the charge traps between vdW materials that are caused by the large concentration difference of majority carriers. However, in case of vdW heterostructure, the subsequently increased leakage current makes the junction less ideal. Thereby interface engineering methods should be used with caution to tune vdW heterostructures on the nanoscale.