Enhanced Performance of a Monolayer MoS/WSe Heterojunction as a Photoelectrochemical Cathode.

Transition-metal dichalcogenide (TMD) semiconductors have attracted interest as photoelectrochemical (PEC) electrodes due to their novel band-gap structures, optoelectronic properties, and photocatalytic activities. However, the photo-harvesting efficiency still requires improvement. In this study, A TMD stacked heterojunction structure was adopted to further enhance the performance of the PEC cathode. A -type WSe and an -type MoS monolayer were stacked layer-by-layer to build a ultrathin vertical heterojunction using a micro-fabrication method. In situ measurement was employed to characterize the intrinsic PEC performance on a single-sheet heterostructure. Benefitting from its built-in electric field and type II band alignment, the MoS/WSe bilayer heterojunction exhibited exceptional photocatalytic activity and a high incident photo-to-current conversion efficiency (IPCE). Comparing with the monolayer WSe cathode, the PEC current and the IPCE of the bilayer heterojunction increased by a factor of 5.6 and enhanced 50%, respectively. The intriguing performance renders the MoS/WSe heterojunction attractive for application in high-performance PEC water splitting.