  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.
