Modification of degenerative photoluminescence in aged monolayer WS₂ by PC₆₁BM surface processing

Owing to their unique physical properties, monolayer transition metal dichalcogenides (TMDCs) have been widely used in applications of light-emitting diodes (LEDs). However, monolayers of TMDCs undergo dramatic aging effects, including intense degradation in optical behavior, extensive cracking, and severe quenching of the direct gap photoluminescence (PL), seriously limiting the device performance. In this work, we show that monolayer WS₂ stored for three months even in the glovebox exhibits obvious degenerative PL with changed peak position that can be attributed to the presence of a large number of trions induced by the aging effect. PC₆₁BM surface processing was used to modify the surface of the aged monolayer WS₂. As expected, higher uniformity in the PL spectrum was obtained. Besides, the PL peak wavelength was modified to be the same as that of the nonaged one and did not change even at higher excitation power. This strategy is shown to successfully suppress the formation of the trion by transferring the excess electrons from WS₂ to PC₆₁BM. The results demonstrate the feasibility of applying PC₆₁BM surface modification to improve the performance of the LED based on monolayer WS₂.