Photodetectors based on 2D materials have been intensively investigated in recent years.34, 35, 36, 37 They show great potential for broadband, high‐sensitivity, and flexible photodetection due to the large light absorption and ultrathin thickness.34, 38 Although the gapless band structure of graphene offers the capability of ultrawide band detection, the short lifetimes of the photogenerated carriers in graphene (in the ps range) hinder the improvement of photocurrent.36, 39, 40 In comparison to graphene, TMDs such as MoS2 and MoSe2 possess large bandgap and thus higher carrier lifetimes, making them as promising candidates for high‐sensitivity photodetectors.34, 41, 42 For a practical photodetector, fast response speed is particularly important for the applications such as imaging and optical communication. However, due to the difficulty in controllable doping, most of the TMDs‐based photodetectors have a lateral device structure of metal‐semiconductor‐metal (MSM) or phototransistor. The transit time of carriers between two contact electrodes limits the device response speed.34 Moreover, the mono‐/multilayer structure of the nanosheets makes them very susceptible to the surface contamination or molecule adsorption, which also degrades the respond speed due to the carrier trapping/detrapping process.