Inhibited nonradiative decay at all exciton densities in monolayer semiconductors

TL;DR

Applying minimal mechanical strain to monolayer TMDCs suppresses nonradiative exciton-exciton annihilation, maintaining near-unity photoluminescence quantum yield across all exciton densities, which could enhance optoelectronic device efficiency.

Contribution

Demonstrated that small mechanical strain can suppress nonradiative decay in monolayer TMDCs, enabling high-efficiency light emission at all exciton densities.

Findings

Strain suppresses exciton-exciton annihilation in TMDC monolayers.

Near-unity PL quantum yield maintained at all exciton densities.

Strain application circumvents VHS resonance effects.

Abstract

Most optoelectronic devices operate at high photocarrier densities, where all semiconductors suffer from enhanced nonradiative recombination. Nonradiative processes proportionately reduce photoluminescence (PL) quantum yield (QY), a performance metric that directly dictates the maximum device efficiency. Although transition-metal dichalcogenide (TMDC) monolayers exhibit near-unity PL QY at low exciton densities, nonradiative exciton-exciton annihilation (EEA) enhanced by van-Hove singularity (VHS) rapidly degrades their PL QY at high exciton densities and limits their utility in practical applications. Here, by applying small mechanical strain (< 1%), we circumvent VHS resonance and drastically suppress EEA in monolayer TMDCs, resulting in near-unity PL QY at all exciton densities despite the presence of a high native defect density. Our findings can enable light-emitting devices that retain high efficiency at all brightnesses.