Five-Ring Fused Tetracyanothienoquinoids as High-Performance
and Solution-Processable n‑Channel Organic Semiconductors:
Effect of the Branching Position of Alkyl Chains
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Abstract
Dicyanomethylene-substituted quinoidal
dithieno[2,3-<i>d</i>;2′,3′-<i>d</i>′]benzo[1,2-<i>b</i>;4,5-<i>b</i>′]dithiophene
compounds (<b>QDTBDT</b>s) with alkyl chains branched at different
positions
were synthesized. Thin-film transistor characteristics showed that
the type of charge carriers in <b>QDTBDT</b>s could be tuned
by changing the branching position of the alkyl chains. <b>QDTBDT-2C</b> exhibited n-channel behavior, and the observed electron mobility
was 0.57 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> without post-treatment, one of the highest values reported for spin-coated
thin-film transistors with no annealing under ambient conditions. <b>QDTBDT-4C</b>-based transistors displayed electron-dominated ambipolar
transport behavior, with electron mobilities reaching 0.2 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> and hole mobilities
in the range of 10<sup>–3</sup>–10<sup>–4</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. <b>QDTBDT-3C</b> showed solution-concentration-dependent carrier
transport characteristics, exhibiting n-type behavior at low solution
concentrations and ambipolar performance at high solution concentrations
with an electron mobility of 0.22 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> and a hole mobility of 0.034 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. CMOS-like inverters
fabricated from <b>QDTBDT-2C</b> displayed high gain and high
noise margins