Removing Defects in WSe₂ via Surface Oxidation and Etching to Improve Solar Conversion Performance

Layered metal dichalcogenide materials (MX2) have great potential for solar energy conversion. However, as-grown MX2 materials often contain edge and terrace defects that degrade semiconducting properties and hinder their solar performance. Herein, we demonstrate a simple approach to removing surface defects and improving the solar performance by using UV-generated ozone to oxidize the surface of WSe2 nanoplates and single crystals, followed by a simple soak in aqueous solutions to remove the oxide. Structural characterizations reveal that defective edges and basal plane defect sites are selectively oxidized and subsequently etched, and the ratio of the nonstoichiometric WSex species is reduced. After this treatment, p-type WSe2 single crystals show increased electron accumulation on the surface and significantly enhanced photoelectrochemical solar conversion efficiency. These results and insights will be useful in the improvement and utilization of layered MX2 materials based on both Se and S for solar energy conversion and other device applications.