High performance transistors via aligned polyfluorene-sorted carbon nanotubes

We evaluate the performance of exceptionally electronic-type sorted, semiconducting, aligned single-walled carbon nanotubes (s-SWCNTs) in field effect transistors (FETs). High on-conductance and high on/off conductance modulation are simultaneously achieved at channel lengths which are both shorter and longer than individual s-SWCNTs. The s-SWCNTs are isolated from heterogeneous mixtures using a polyfluorene-derivative as a selective agent and aligned on substrates via dose-controlled, floating evaporative self-assembly at densities of ∼50 s-SWCNTs μm⁻¹. At a channel length of 9 μm the s-SWCNTs percolate to span the FET channel, and the on/off ratio and charge transport mobility are 2.2 × 10⁷ and 46 cm² V⁻¹ s⁻¹, respectively. At a channel length of 400 nm, a large fraction of the s-SWCNTs directly span the channel, and the on-conductance per width is 61 μS μm⁻¹ and the on/off ratio is 4 × 10⁵. These results are considerably better than previous solution-processed FETs, which have suffered from poor on/off ratio due to spurious metallic nanotubes that bridge the channel. 4071 individual and small bundles of s-SWCNTs are tested in 400 nm channel length FETs, and all show semiconducting behavior, demonstrating the high fidelity of polyfluorenes as selective agents and the promise of assembling s-SWCNTs from solution to create high performance semiconductor electronic devices.