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

Abstract

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 (∼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_MoS₂ ≈ 11 cm² V^-1 s^-1, μ_WS₂ ≈ 9 cm² V^-1 s^-1, and μ_WSe₂ ≈ 2 cm² V^-1 s^-1 with a current on/off ratios of <i>I</i>_on/<i>I</i>_off ≈ 2.6 × 10³, 3.4 × 10³, and 4.2 × 10⁴ for MoS₂, WS₂, and WSe₂, 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 WSe₂ transistors is maintained on polyethylene terephthalate (PET) even after 1000 bending cycles at 1% strain.