# Doping Carbon Nanotube Ethylene-Vinyl Acetate Thin Films for Touch-Sensitive Applications

## TL;DR

This paper explores using carbon nanotube films as a flexible and transparent alternative to traditional materials in touch-sensitive devices.

## Contribution

The study introduces CuCl2 as a low-cost p-doping alternative and demonstrates touch-sensitive devices with high transparency and performance.

## Key findings

- Optimized single-walled carbon nanotube films show no percolation effects down to 5 nm thickness.
- Doped films achieve a 10 on/off ratio at 95% optical transmittance in touch-sensitive devices.
- Sheet resistance and on/off ratio have a linear relationship, enabling threshold thickness determination.

## Abstract

Transparent conductive
films are key components of many
optoelectronic
devices but are often made from either scarce or brittle materials
like indium tin oxide. Carbon nanotube-polymer films offer an abundant
and flexible alternative. Here, we report how the dimensions of the
carbon nanotube raw material affect their thin film performance and
thickness yield when processed with the polymer ethylene-vinyl acetate.
We perform chemical doping with several halogenated metals and find
the electron affinity of the metal to be a good indicator of p-doping
effectiveness. We identify CuCl2 as low-cost alternative
to the established gold chloride dopants. Optimising the dopant deposition
method allows us to reduce the effect of doping on the optical transmittance.
Percolation analysis of our films demonstrates that optimized single-walled
carbon nanotube-ethylene-vinyl acetate films show no sign of percolation
effects down to thicknesses of 5 nm. Finally, we produce transparent
touch-sensitive devices. Comparing several of these devices, we find
a linear relationship between the sheet resistance and the on/off
ratio of the touch sensing that can be used to determine a threshold
film thickness. Using doped carbon nanotube-ethylene-vinyl acetate
films increases the on/off ratio and allows us to fabricate touch-sensitive
devices with an on/off ratio of 10 at 95% optical transmittance. This
clearly demonstrates the potential of these films for transparent
touch-sensitive applications.