In detail, upon illumination by the 1560 nm laser, electrons and holes in graphene are rapidly injected into the adjacent WS2 layer (Figure ). After that, a fraction of the hot electrons cool in several picoseconds, inducing an ultrafast intrinsic response peak in the 2PC signal (Figure ⅱ, upper panel). Meanwhile, the injected holes are captured by the defects at the surface of WS2, which not only leads to a relatively long circulation of the electrons, reflected by the slow intrinsic response dip in the 2PC signal (Figure ⅱ, lower plane), but also contributes to a high responsivity of 0.26 A/W (see Supporting Information Section 6 for detailed calculations). In comparison, a device without the slow dip component possesses one order of magnitude lower responsivity under the same measurement condition (Supporting Information Section 7). In addition, upon increasing the external bias, the dip can be almost entirely suppressed (Figure ), presumably due to the depopulation of traps.