Measurement of Quantum Yields of Monolayer TMDs Using Dye-Dispersed PMMA Thin Films

Abstract

In general, the quantum yields (QYs) of monolayer transition metal dichalcogenides (1L-TMDs) are low, typically less than 1% in their pristine state, significantly limiting their photonic applications. Many methods have been reported to increase the QYs of 1L-TMDs; however, the technical difficulties involved in the reliable estimation of these QYs have prevented the general assessment of these methods. Herein, we demonstrate the estimation of the QYs of 1L-TMDs using a poly methyl methacrylate (PMMA) thin film embedded with rhodamine 6G (R6G) as a reference specimen for measuring the QYs of 1L-TMDs. The PMMA/R6G composite films with thicknesses of 80 and 300 nm demonstrated spatially homogeneous emissions with the incorporation of well-dispersed R6G molecules, and may, therefore, be used as ideal reference specimens for the QY measurement of 1L-TMDs. Using our reference specimens, for which the QY ranged from 5.4% to 22.2% depending on the film thickness and R6G concentrations, we measured the QYs of the exfoliated or chemical vapor deposition (CVD)-grown 1L-WS2, -MoSe2, -MoS2, and -WSe2 TMDs. The convenient procedure proposed in this study for preparing the thin reference films and the simple protocol for the QY estimation of 1L-TMDs may enable accurate comparisons of the absolute QYs between the 1L-TMD samples, thereby enabling the development of a method to improve the QY of 1L-TMDs.

Upconversion Photovoltaic Effect of WS2/2D Perovskite Heterostructures by Two-Photon Absorption

“…Compared to other TMDCs, WS 2 monolayers have a relatively higher PL quantum yield. 38 a high PL quantum yield. 13 Hence, WS 2 monolayer/PEPI vertical heterostructures are chosen as the system for investigating the upconversion photovoltaic effect.…”

Highly Photoluminescent Monolayer MoS2 and WS2 Achieved via Superacid Assisted Vacancy Reparation and Doping Strategy

“…PL QYs of these samples were measured and calculated by using a poly(methyl methacrylate) (PMMA) thin film embedded with Rhodamine 6G molecules (QY ≈57.4%) as reference (see Note S2 and Figure S4 for detailed description, Supporting Information). [ 2a ] Figure 2d shows that the PL QY of pristine 1L‐MoS 2 is rather low (≈0.2%). The maximum PL QY of ≈14.1% is achieved from the TFMS (60 µL) treated 1L‐MoS 2 sample.…”

“…Table 1 summarizes the reported fluorescence performance of various chemically‐treated TMDs, indicating our results are the relatively higher PL QY levels for CVD‐grown 1L samples up to now. [ 2c,21 ]…”

“…Similar results have also been observed in the cases of TFSI‐ and thiolate‐repaired 1L‐MoS 2 . [ 2c,26 ]…”

“…[ 1 ] Compared with mechanically exfoliated TMDs, the photoluminescence quantum yield (PL QY) of CVD‐grown samples is much lower (≈0.01–6%) due to the existence of abundant sulfur vacancy defects. [ 2 ] Previous studies revealed that these sulfur vacancies can act as donor defects and create midgap trap states within the bandgap, capturing charge carriers and quenching PL emission. [ 3 ] Therefore, effective reduction of sulfur vacancies is imperative to achieve high‐performance two‐dimensional (2D) optoelectronic devices based on TMDs materials.…”