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

The investigation of high-mobility two-dimensional (2D) flakes beyond molybdenum disulfide (MoS 2 ) 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 (WSe 2 ) and tungsten disulfide (WS 2 ) as well as MoS 2 as a comparison. We use Langmuir-Schaefer coating to achieve highly aligned and conformal flake networks, with minimal mesoporosity (∼2-5%), at low processing temperatures (120 °C) and without acid treatments. This allows us to fabricate electrochemical transistors in ambient air, achieving average mobilities of μ MoS 2 ≈ 11 cm 2 V -1 s -1 , μ WS 2 ≈ 9 cm 2 V -1 s -1 , and μ WSe 2 ≈ 2 cm 2 V -1 s -1 with a current on/off ratios of I on / I off ≈ 2.6 × 10 3 , 3.4 × 10 3 , and 4.2 × 10 4 for MoS 2 , WS 2 , and WSe 2 , respectively. Moreover, our transistors display threshold voltages near ∼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 WSe 2 transistors is maintained on polyethylene terephthalate (PET) even after 1000 bending cycles at 1% strain.