(a) The schematic diagram of a hybrid graphene–PbS QDs phototransistor. (b) The energy band diagram at the graphene/PbS QDs interface. (c) The linear dependence of the photocurrent on the applied drain-source voltage for different optical powers (46, 336, 516 pW). V_BG=0. Inset: total current (I=I_dark+I_photo) as a function of the applied drain-source voltage for different optical powers. (d) The responsivity as a function of the applied back-gate voltage V_BG. V_SD=5 V. Reproduced from Ref. [32] with permission from the Nature Publishing Group.