Multiflake Thin Film Electronic Devices of Solution Processed 2D MoS2 Enabled by Sonopolymer Assisted Exfoliation and Surface Modification

Abstract

The solvent-assisted exfoliation of transition metal dichalchogenides (TMDs) is a promising method for preparing scalable quantities of two-dimensional nanomaterials dispersed in a liquid phase. However, low concentrations and the restacking/aggregation of TMD layers remain challenges to the solution based preparation of large-area electronic devices. Here we present advances in the exfoliation and solution processing of 2D MoS2 that are subsequently leveraged to prepare and electronically probe homogeneous multiflake thin-film devices. We report that sonopolymer, formed when using 1,2-dichlorobenzene (DCB) as a solvent, plays a critical role in affording stable dispersions (up to 0.5 mg mL–1) of few-layer MoS2 flakes in the 2H phase after only 6 h of low-power sonication. After removing the sonopolymer using a washing procedure, alkyl-trichlorosilane surfactants were used to prevent the restacking of 2D MoS2 layers and create stable dispersions with concentrations as high as 85 mg mL–1. In spin-coated multiflake thin films as thin as 20 nm, electron transport parallel to the substrate was quantifiable over channel lengths of 50 μm owing to the homogeneous film formation. By further varying the alkyl-trichlorosilane chain length we show that a trade-off between dispersibility (film homogeneity) and electronic insulation from the surfactant leads to a maximum (multiflake) electron mobility of 0.02 cm2 V–1 s–1 using hexyl-trichlorosilane modified MoS2 in the direction perpendicular to the substrate as measured by space-charge limited current devices.