A general figure of merit for thick and thin transparent conductive carbon nanotube coatings

TL;DR

This paper introduces a wavelength-dependent figure of merit for transparent nanotube coatings, considering realistic optical and electrical properties, and provides a practical method to optimize their thickness and treatment for desired transparency and conductivity.

Contribution

It proposes a new figure of merit based on optical density and sheet resistance that accounts for realistic nanotube properties, improving evaluation of transparent conductive coatings.

Findings

Correlation between metal enrichment and figure of merit.

Graphical method to optimize layer thickness or treatment.

Applicability to oxide coatings.

Abstract

We suggest a wavelength-dependent figure of merit for transparent conducting nanotube networks, composed of the sheet resistance and the optical density. We argue that this would be more useful than other suggestions prevailing in the literature, because it relies on more realistic assumptions regarding the optical parameters of real nanotubes: it takes into account the fact that the dc resistivity depends on the concentration of free carriers, while the visible absorption is caused by bound carriers. Based on sheet resistance measurements and wide-range transmission spectra, we compare several commercial nanotube types and find correlation between metal enrichment and figure of merit. A simple graphical approach is suggested to determine if the required optical and transport properties can be achieved by varying the thickness of the nanotube layer or a more aggressive treatment is needed. The procedure can be extended to oxide coatings as well.