The bright side of defects in MoS$_2$ and WS$_2$ and a generalizable chemical treatment protocol for defect passivation

TL;DR

This study reveals sulfur vacancies in MoS$_2$ and WS$_2$ act as exciton traps and introduces a chemical protocol using thiols or sulfides with Lewis acids to effectively passivate these defects, significantly enhancing photoluminescence.

Contribution

The paper presents a novel, generalizable chemical treatment protocol for defect passivation in monolayer MoS$_2$ and WS$_2$, improving optoelectronic properties without reducing mobility.

Findings

Sulfur vacancies trap excitons, impairing photoluminescence.

Current treatments fail to passivate sulfur vacancies effectively.

The new protocol boosts photoluminescence up to 275-fold while maintaining mobility.

Abstract

Structural defects are widely regarded as detrimental to the optoelectronic properties of monolayer transition metal dichalcogenides, leading to concerted efforts to eliminate defects via improved materials growth or post-growth passivation. Here, using steady-state and ultrafast optical spectroscopy, supported by ab initio calculations, we demonstrate that sulfur vacancy defects act as exciton traps. Current chemical treatments do not passivate these sites, leading to decreased mobility and trap-limited photoluminescence. We present a generalizable treatment protocol based on the use of passivating agents such as thiols or sulfides in combination with a Lewis acid to passivate sulfur vacancies in monolayer MoS$_2$ and WS$_2$, increasing photoluminescence up to 275 fold, while maintaining mobilities. Our findings suggest a route for simple and rational defect engineering strategies, where the passivating agent varies the electronic properties, thereby allowing the design of new heterostructures.