Uncovering the ultimate performance of single-walled carbon nanotube films as transparent conductors

TL;DR

This study demonstrates that smaller SWCNT bundles enhance the performance of transparent conductive films, providing experimental evidence and a semi-empirical model to estimate their ultimate conductivity and transparency limits.

Contribution

It offers direct experimental evidence linking SWCNT bundling to performance degradation and introduces a semi-empirical model for predicting ultimate TCF performance based on bundle size and length.

Findings

Smaller SWCNT bundles improve network interconnectivity.

Larger bundles lead to higher sheet resistance.

Estimated ultimate performance is around 80 Ohms/sq. at 90% transparency.

Abstract

The ultimate performance - ratio of electrical conductivity to optical absorbance - of single- walled carbon nanotube (SWCNTs) transparent conductive films (TCFs) is an issue of considerable application relevance. Here, we present direct experimental evidence that SWCNT bundling is detrimental for their performance. We combine floating catalyst synthesis of non-bundled, high-quality SWCNTs with an aggregation chamber, in which bundles with mean diameters ranging from 1.38 to 2.90 nm are formed from identical 3 microns long SWCNTs. The as-deposited TCFs from 1.38 nm bundles showed sheet resistances of 310 Ohms/sq. at 90% transparency, while those from larger bundles of 1.80 and 2.90 nm only reached values of 475 and 670 Ohms/sq., respectively. Based on these observations, we elucidate how networks formed by smaller bundles perform better due to their greater interconnectivity at a given optical density. Finally, we present a semi-empirical model for TCF performance as a function of SWCNT mean length and bundle diameter. This gives an estimate for the ultimate performance of non-doped, random network mixed-metallicity SWCNT TCFs at ~80 Ohms/sq. and 90% transparency.