Roll-to-Roll Deposition of Semiconducting 2D Nanoflake Films of Transition Metal Dichalcogenides for Optoelectronic Applications

Abstract

Exfoliated transition metal dichalcogenide (TMD) nanomaterials possess remarkable and tunable semiconducting properties which make them competitive for use in ultrathin, flexible devices such as photodetectors, sensors, and photoelectrodes for solar energy conversion. Until now, the large-scale production of such devices has presented a challenge that limits their commercialization and broad application. We demonstrate here, for the first time, a procedure for the roll-to-roll (R2R) deposition of two-dimensional (2D) TMD nanoflake thin films via a continuous liquid–liquid interfacial self-assembly method. Remarkably, no solvent removal is required during film deposition, nor is there any nanoflake accumulation in the solvent bath, making continuous operation feasible. In our prototype deposition system described herein, TMD nanoflakes (9 nm average flake thickness, 50–500 nm long) are self-assembled into large area films up to 100 mm in width that are reproducibly printed at 10 mm s–1 with nanoflake loadings of 35 mg m–2. Optically uniform coverage on transparent conductive oxide-coated flexible plastic substrates is shown, and key printing parameters to afford the required single-flake-layer deposition are identified. Photoelectrochemical testing verifies optoelectronic activity of the MoS2 nanoflake films achieving photocurrent densities for iodide oxidation of 40 μA cm–2 at +0.1 V (vs an Ag/Ag+ reference) under 1 sun illumination. In addition, we show that these R2R films are robust and that our method works for multiple (successive) flake layer depositions by preparing large area MoS2/WSe2 heterojunction nanoflake films. This demonstration represents an important milestone in advancing large-scale production of 2D TMD films toward low-cost, high-performance optoelectronic devices.

Liquid–liquid interfaces: a unique and advantageous environment to prepare and process thin films of complex materials

“…Focusing on the real applicability of the technique, it becomes clear that the LLIR has huge potential to be used in large-scale production of thin films, aiming at industrially scaled production. The roll-to-roll continuous deposition technique reported recently was the first real demonstration of this possibility, 57 but several other approaches can be developed by scientists and engineers willing to dedicate work to that.…”

“…5f and g). 57 The exfoliated TMDs were dispersed in butanol and continuously injected in the aqueous phase in an n-heptane/ water biphasic system. Butanol, less dense than water, carries the TMD nanoflakes to the n-heptane/water interface, resulting in the self-assembled film.…”

“…5f and g). 57 This deposition apparatus represents an important step towards industrial application of the LLIR technique. (4) ethylene glycol removal and film deposition; and (5) drying; 56 and (e) photograph of a single-flake-layer WSe 2 thin film deposited on flexible ITOcoated PET plastic.…”

“…56 Copyright Springer Nature, 2015. (f) Schematic side view of the roll-to-roll deposition apparatus; 57 and (g) photograph of the rollto-roll deposition apparatus, where the inset gives a close-up overhead view. 57 Copyright American Chemical Society.…”

Liquid‐Exfoliated 2D Materials for Optoelectronic Applications

“…Although study on liquid-exfoliated transition metal dichalcogenides (TMD) for photodetector application is still in its infancy compared to rGO and GQD-based photodetectors, TMD photodetectors are gaining increased popularity recently as the number of literatures on TMD photodetectors are growing significantly either reported as single materials [150][151][152][153][154][155][156][157][158][399][400][401][402][403][404][405][406][407][408] or forming composites with polymers or other nanomaterials. [68,161,162,[409][410][411] One of the reasons of TMD popularity is that TMDs possess many interesting properties that other 2D materials do not have.…”