and a generalizable chemical treatment protocol for defect passivation

Defects in transition metal dichalcogenides, such as MoS₂ and WS₂, are frequently considered responsible for quenching photoluminescence (PL) and lowering mobility, limiting many of the proposed applications. However, while many chemical treatments have been proposed to passivate defects, primarily assumed to be sulfur vacancies, the mechanism of this passivation is poorly understood. In this work, we illustrate how TFSI superacid treatment reveals an optical subgap state associated with sulfur vacancies. At room temperature, this subgap state contributes to enhanced quantum yields and lengthened emission lifetimes, compared to untreated samples, rather than quenching PL. Building on this understanding, we propose a generalizable treatment protocol to passivate defects in monolayer MoS₂ and WS₂, increasing photoluminescence and maintaining mobilities. This protocol opens up a route for solution-based, post-processing of samples, which could not only passivate defects, but also simultaneously tune properties and functionalize materials.