Fabrication of a MoS2/Graphene Nanoribbon Heterojunction Network for Improved Thermoelectric Properties

A number of 2D materials have been developed that have properties different from bulk materials due to the quantum confinement effect. These 2D materials can also form a vertical van der Waals heterojunction at a large interface with other 2D materials, resulting in unique electronic and thermoelectric properties. However, it is difficult to fabricate a van der Waals heterostructure of 2D materials that can provide a sufficient temperature gradient while also forming carrier paths across the vertical heterojunction. Here, a heterojunction network structure constructed of highly conductive sub‐20‐nm graphene nanoribbons (GNRs) arrays stacked on a semiconducting molybdenum disulfide (MoS2) monolayer is suggested to maximize the heterojunction effect on carrier transport. This heterojunction network allows the carriers inevitably pass back and forth between the GNR and the MoS2 through the vertical heterojunction, effectively utilizing the interfacial properties in thermoelectricity. This structure also can modify the band structure by controlling the linewidth of the nanoribbons, or introduce an interlayer at the heterojunctions to enhance the tunneling effect between the two layers, thus significantly improved thermoelectric properties are achieved such as enhanced electrical conductivity of 700 S m−1 and a high power factor of 222 µW m−1 K−1. A new type of heterojunction network of randomly oriented pseudo‐1D graphene nanoribbon (GNR) arrays on a 2D MoS2 monolayer, fabricated through block copolymer (BCP) lithography and a repeated transfer process, is proposed. The GNR/MoS2 heterojunction network shows improved electric conductivity and thermoelectric properties, as this vertical heterojunction structure efficiently forms carrier conduction paths that facilitate carrier‐controlled transport.