Charge Transport in Mixed Semiconducting SWCNT Networks with Tailored Diameter Distributions

Abstract

The recent availability of purely semiconducting single-walled carbon nanotubes (SWCNTs) and the ability to prepare dense and uniform SWCNT networks from dispersion has led to promising applications in optoelectronics, e.g. in field-effect transistors (FETs), light-emitting diodes, notch filters and solar cells. Further optimization and controlled tuning of nanotube networks is desirable to establish them as competitive semiconducting materials. The impact of the SWCNT network composition on the overall charge transport was demonstrated recently [1]. The uneven energy landscape of networks with a broad tube diameter and thus bandgap distribution results in inferior transport properties. Contrary to common belief, the charge transport in networks is not solely determined by tube-tube junctions but intra-nanotube transport also has a significant impact on the overall network mobility. Here, we examine this hypothesis in a detailed charge transport study of FETs with SWCNT networks consisting of polymer-sorted small diameter (6,5) SWCNTs (0.76 nm) and large diameter plasma torch SWCNTs (1.2-1.5 nm) with different but controlled mixing ratios. All FETs showed balanced ambipolar transport with low off-currents and negligible hysteresis. The extracted mobilities varied characteristically with network composition. The obtained experimental data are compared to results from numerically simulated networks with analogous SWCNT compositions. The employed random resistor network model was recently shown to adequately describe the carrier density-dependent mobility in SWCNT networks [2]. [1] M Brohmann et al., J. Phys Chem. C 122, 19886-19896 (2018) [2] S. P. Schießl et al., Phys. Rev. Mater. 1, 046003 (2017) Figure 1