a) Schematic illustration shows the rapid separation and transport of electrons and holes along the in‐plane direction of MoSe2 under pulsed light illumination. The electrons were collected by graphene transparent electrode, ensuring the fast transport of electrons to the outside electrical circuit. Variation of photovoltage is monitored by an oscilloscope to determine the response speed. Photoresponse of the self‐powered photodetector to pulsed light illumination with varied frequency of b) 1 kHz, and c) 1 MHz. d) Enlarged photoresponse curve at 1 MHz. Rise time (t r) and fall time (t f) are the time intervals between 10% and 90% of peak response. Response curve of the 650 nm LD light source is also shown in the upper part of the figure for comparison. e) Photoresponse of the MoSe2/Si heterojunction with and without graphene transparent electrode under pulsed light illumination. f) Relative balance (V max–V min)/V max versus switching frequency of the devices with and without graphene.