High-Mobility Flexible Transistors with Low- Temperature Solution-Processed Tungsten Dichalcogenides

The investigation of high-mobility two-dimensional (2D) flakes beyond molybdenum disulfide (MoS2) will be necessary to create a library of high-mobility solution-processed networks that conform to substrates and remain functional over thousands of bending cycles. Here we report electrochemical exfoliation of large-aspect-ratio (>100) semiconducting flakes of tungsten diselenide (WSe2) and tungsten disulfide (WS2) as well as MoS2 as a comparison. We use Langmuir- Schaefer coating to achieve highly aligned and conformal flake networks, with minimal mesoporosity (similar to 2-5%), at low processing temperatures (120 degrees C) and without acid treatments. This allows us to fabricate electrochemical transistors in ambient air, achieving average mobilities of mu MoS2 approximate to 11 cm2 V-1 s-1, mu WS2 approximate to 9 cm2 V-1 s-1, and mu WSe2 approximate to 2 cm2 V-1 s-1 with a current on/off ratios of Ion/Ioff approximate to 2.6 x 103, 3.4 x 103, and 4.2 x 104 for MoS2, WS2, and WSe2, respectively. Moreover, our transistors display threshold voltages near similar to 0.4 V with subthreshold slopes as low as 182 mV/dec, which are essential factors in maintaining power efficiency and represent a 1 order of magnitude improvement in the state of the art. Furthermore, the performance of our WSe2 transistors is maintained on polyethylene terephthalate (PET) even after 1000 bending cycles at 1% strain.

Automated summary

This study presents a method to obtain large-area semiconducting flakes of tungsten diselenide (WSe2) and tungsten disulfide (WS2) through electrochemical exfoliation. The flakes are then aligned and conformal using Langmuir-Schaefer coating technique. The fabricated electrochemical transistors exhibit high mobility and good performance on bending substrates, making them potentially valuable for flexible electronics applications.