Monolayer MoS2 heterojunction solar cells.

We realized photovoltaic operation in large-scale MoS2 monolayers by the formation of a type-II heterojunction with p-Si. The MoS2 monolayer introduces a built-in electric field near the interface between MoS2 and p-Si to help photogenerated carrier separation. Such a heterojunction photovoltaic device achieves a power conversion efficiency of 5.23%, which is the highest efficiency among all monolayer transition-metal dichalcogenide-based solar cells. The demonstrated results of monolayer MoS2/Si-based solar cells hold the promise for integration of 2D materials with commercially available Si-based electronics in highly efficient devices.