Defect‐Dependent Optoelectronic Properties at a Molecular p‐dopant/Monolayer WS2 Interface

Abstract

Combining transition metal dichalcogenides (TMDCs) and molecular semiconductors is an attractive route for forming van der Waals heterostructures with optoelectronic properties not found in either component. Herein, the strong p‐type molecular dopant, 1,3,4,5,7,8‐hexafluoro‐tetracyano naphthoquinodimethane (F6TCNNQ), is utilized to form a van der Waals interface with a WS2 monolayer chemical vapor deposition grown on sapphire, which is characterized with angle‐resolved photoelectron and UV‐visible absorption spectroscopy. The interface formed by F6TCNNQ and the as‐grown WS2 monolayer (ML‐WS2) shows no sign of strong interaction or charge transfer. In contrast, defects formed by annealing of ML‐WS2 at 1000 K (d‐ML‐WS2) induce strong n‐type doping of the TMDC. Subsequent F6TCNNQ adsorption on d‐ML‐WS2 is then accompanied by pronounced charge transfer resulting in the formation of interface F6TCNNQ anions and an interface optical transition at 1.5 eV, possibly attributed to an interlayer excitonic state. It is shown in the results that the presence of defects within TMDC monolayers can substantially modify not only the TMDC electronic properties, but also the ground and excited states of their interface with organic molecular dopants. This demonstrates an additional degree of freedom for designing tailored (opto‐)electronic properties based on the combination of TMDCs and molecular semiconductors.