Exploring the Optoelectronic Properties of Solution Processed 2D TMD Nanoflakes Exfoliated Via Large Molecule Electrointercalation

Abstract

The remarkable semiconducting properties of 2D transition metal dicalcogenides (TMDs) are of great interest to researchers hoping to harness such traits for optoelectronic and photoelectrochemical (PEC) applications. 2D MoS2, WSe2, and related materials have been incorporated in ultrathin devices including transistors1, LEDs2, solar cells3, and photoelectrodes4,5. While typical approaches like chemical vapor deposition produce pristine monolayer or few-layer 2D TMD sheets and flakes, these methods are expensive and energy intensive making them unsuitable for large scale implementation. Thus, developing scalable solution processable methods to prepare high-quality 2D TMD materials is crucial.Typical solution-based production approaches have historically yielded TMDs with poor semiconducting behavior. Recently a novel electrointercalation technique was reported by Lin et al. wherein large organic cations are inserted in between MoS2 layers in a bulk single crystal thereby exfoliating it to thin nanoflakes while maintaining benchmark semiconducting performance. Despite this advance, there remains a lack of information concerning the optoelectronic properties of these flakes and their ability to be used in solar energy conversion devices.Herein we use the electrointercalation of large cation tetraheptylammonium bromide (THAB) to exfoliate a variety of bulk TMDs, investigate their optoelectronic properties, and process them into photoelectrodes for solar-to-chemical energy conversion. When compared to alternative solution processing methods such as ultrasonication and shear-mixing exfoliation, these THAB-assisted exfoliated flakes show increased photocurrents, photovoltages, and internal quantum efficiencies. We show that this is, in part, a result of thinner 2D flakes with larger lateral dimensions. Raman, photoluminescence, and X-ray spectroscopy suggest that this technique results in a lower defect density when compared to traditional methods. These results suggest that THAB-intercalated 2D TMDs are promising for scalable solar energy applications.