Layer-Number-Dependent Electronic and Optoelectronic Properties of 2D WSe2-Organic Hybrid Heterojunction

One of the most attractive features of 2D WSe2 is a tunability in its electronic and optoelectronic properties depending on the layer number. To harness such unique characteristics for device applications, high quality and easily processable heterojunctions are required and relevant layer-number-dependent properties must be understood. Herein, a study is reported on hybrid heterojunctions between 2D WSe2 and organic molecules from one-step solution chemistry and their layer-number-dependent properties. Eosin Y (EY) dye is selected as a p-dopant and uniformly stacked on mechanically exfoliated WSe2 flakes via van der Waals interaction, forming a hybrid heterojunction with a type II alignment. The EY-WSe2 heterojunction shows significantly enhanced currents compared to pristine WSe2 with a lower barrier height and a longer effective screening length. The work function of the heterostructure is also lower than that of pristine WSe2. The efficient exciton dissociation and doping effect by EY are confirmed by photocurrent and photoluminescence measurements, where WSe2 emission is markedly quenched by EY and exciton contribution decreases with layer number. These findings shed critical insights into layer-number-dependent electronic and optoelectronic properties of organic-WSe2 layers and also provide simple yet effective means to construct transition metal dichalcogenide-based heterostructures, which should be valuable for developing layered 2D devices.