Monolayer WS₂ electro- and photo-luminescence enhancement by TFSI treatment

Abstract

Layered material heterostructures (LMHs) can be used to fabricate electroluminescent devices operating in the visible spectral region. A major advantage of LMH-light emitting diodes (LEDs) is that electroluminescence (EL) emission can be tuned across that of different exciton complexes (e.g. biexcitons, trions, quintons) by controlling the charge density. However, these devices have an EL quantum
efficiency as low as~10−4%. Here, we show that the superacid bis-(triuoromethane)sulfonimide (TFSI) treatment of monolayer WS2-LEDs boosts EL quantum efficiency by over one order of magnitude at room temperature. Non-treated devices emit light mainly from negatively charged excitons, while the emission in treated ones predominantly involves radiative recombination of neutral excitons. This paves the way to tunable and efficient LMH-LEDs.

Ultrafast Coherent Exciton Couplings and Many-Body Interactions in Monolayer WS2

“…To explore exciton couplings in 1L-TMDs, we prepare 1L-WS 2 flakes by micromechanical exfoliation of bulk 2H-WS 2 . Selected flakes are stamped onto a polycrystalline Ag film with a thickness of 200 nm, coated with a 5 nm aluminum oxide layer to avoid hot electron transfer between Ag and TMD. − The samples are characterized by Raman and photoluminescence spectroscopy (see Figure S3 of the Supporting Information, SI).…”