Photophysical comparison of liquid and mechanically exfoliated WS$_2$ monolayers

TL;DR

This study compares the photophysical properties of liquid exfoliated and mechanically exfoliated WS2 monolayers, revealing energy transfer as a key factor in photoluminescence efficiency and highlighting the potential of liquid exfoliated WS2 for optoelectronic applications.

Contribution

It provides a systematic comparison of optical and photophysical properties of liquid and mechanically exfoliated WS2 monolayers, with insights into exciton dynamics and energy transfer effects.

Findings

Energy transfer causes PL quenching in liquid exfoliated WS2

Liquid exfoliated WS2 shows promising optical quality for devices

Ultrafast measurements reveal exciton dynamics differences

Abstract

Semiconducting transition metal dichalcogenides (TMDs) are desired as active materials in optoelectronic devices due to their strong excitonic effects. They can be exfoliated from their parent layered materials with low-cost and for mass production via a liquid exfoliation method. However, the device application of TMDs prepared by liquid phase exfoliation is limited by their poor photoluminescence quantum efficiencies (PLQE). It is crucial to understand the reason to low PLQE for their practical device development. Here we evaluate the quality of monolayer-enriched liquid phase exfoliated (LPE) WS$_2$ dispersions by systematically investigating their optical and photophysical properties and contrasting with mechanically exfoliated (ME) WS2 monolayers. An in-depth understanding of the exciton dynamics is gained with ultrafast pump-probe measurements. We reveal that the energy transfer between monolayer and few-layers in LPE WS$_2$ dispersions is a substantial reason for their quenched PL. In addition, we show that LPE WS$_2$ is promising to build high performance optoelectronic devices with excellent optical quality.