(Invited) Two-Dimensional Layered Materials/Silicon Heterojunctions for Energy and Optoelectronic Applications

Two-dimensional (2D) layered materials such as graphene, metal dichalcogenides, and topological insulators have attracted much attention due to their extraordinary properties. However, their applications in optoelectronic devices are hindered by the relatively low light absorption of monolayer materials as well as difficulties in controllable doping and p-n junction fabrications. In comparison to the formation of homojunctions or heterojunctions, respectively, from one or two different 2D layered materials, the formation of heterojunctions by combining a 2D layered material with a semiconductor offers a feasible and easier way to construct high-performance optoelectronic devices by harnessing the advantages of both materials. Herein, we report a systematic investigation on 2D layered material/silicon heterojunction based photovoltaic and optoelectronic devices. It was found that interface charge recombination and graphene conductivity play important roles in determining solar cell performance. By suppressing surface recombination and optimizing graphene layers and doping level, we demonstrate power conversion efficiencies (PCEs) over 14% for graphene/silicon heterojunctions. A new type of solar cell based on the graphene quantum dots (GQDs)/silicon heterojunctions was also developed. Owing to the extraordinary optical and electrical properties of GQDs, the GQDs/Si heterojunctions show a promising efficiency over 12%. Further, ultra-fast photodetectors were constructed from the MoS₂/Si, MoSe₂/Si, and Bi2SeTe₂/Si heterojunctions. Our work reveals the great potential of two-dimensional layered materials/silicon heterojunctions for high-performance photovoltaic and optoelectronic devices.