Approaching the Limits of Transparency and Conductivity in Graphitic Materials through Lithium Intercalation

TL;DR

This study demonstrates that lithium intercalation in ultrathin graphite significantly enhances both optical transmittance and electrical conductivity, surpassing existing transparent conductor materials and revealing new optoelectronic modification mechanisms.

Contribution

It provides in situ measurements showing simultaneous improvements in transparency and conductivity in ultrathin graphite through lithium intercalation, a novel approach for transparent conductors.

Findings

Optical transmittance increased up to twofold upon intercalation.

Electrical conductivity improved by up to two orders of magnitude.

Achieved a transmission of 91.7% with a sheet resistance of 3.0 Ω/sq.

Abstract

Various bandstructure engineering methods have been studied to improve the performance of graphitic transparent conductors; however none demonstrated an increase of optical transmittance in the visible range. Here we measure in situ optical transmittance spectra and electrical transport properties of ultrathin-graphite (3-60 graphene layers) simultaneously via electrochemical lithiation/delithiation. Upon intercalation we observe an increase of both optical transmittance (up to twofold) and electrical conductivity (up to two orders of magnitude), strikingly different from other materials. Transmission as high as 91.7% with a sheet resistance of 3.0 {\Omega} per square is achieved for 19-layer LiC6, which corresponds to a figure of merit {\sigma}_dc/{\sigma}_opt = 1400, significantly higher than any other continuous transparent electrodes. The unconventional modification of ultrathin-graphite optoelectronic properties is explained by the suppression of interband optical transitions and a small intraband Drude conductivity near the interband edge. Our techniques enable the investigation of other aspects of intercalation in nanostructures.