Abstract

Flexible transparent conducting electrodes (FTCE) are an essential component of next-generation flexible optoelectronic devices. Graphene is expected to be a promising material for the FTCE, because of its high transparency, large charge carrier mobilities, and outstanding chemical and mechanical stability. However, the electrical conductivity of graphene is still not good enough to be used as the electrode of an FTCE, which hinders its practical application. In this study, graphene was heavily n-type doped while maintaining high transmittance by adsorbing amine-rich macromolecules to graphene. The n-type charge-transfer doping of graphene was maximized by increasing the density of free amine in the macromolecule through a vacuum annealing process. The graphene adsorbed with the n-type dopants was stacked twice, resulting in a graphene FTCE with a sheet resistance of 38 ohm/sq and optical transmittance of 94.1%. The figure of merit (FoM) of the graphene electrode is as high as 158, which is significantly higher than the minimum standard for commercially available transparent electrodes (FoM = 35) as well as graphene electrodes doped with previously reported chemical doping methods. Furthermore, the n-doped graphene electrodes not only show outstanding flexibility but also maintain the doping effect even in high temperature (500 K) and high vacuum (~10−6 torr) conditions. These results show that the graphene doping proposed in this study is a promising approach for graphene-based next-generation FTCEs.

Highlights

  • In recent years, flexible transparent conducting electrodes (FTCEs) have attracted tremendous interest due to their pivotal role in foldable, flexible and wearable optoelectronic devices [1]

  • Polyethyleneimine (PEI), an amine-rich macromolecule, can transfer electrons to graphene because its work function

  • Before, graphene can be n-type doped by electron-transfer from lone-pair electrons present in the previous studies forfor graphene doping using nitrogen atoms atoms of of alkyl-amine alkyl-amine[22,23,25,26,27,28]

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Summary

Introduction

Flexible transparent conducting electrodes (FTCEs) have attracted tremendous interest due to their pivotal role in foldable, flexible and wearable optoelectronic devices [1]. For the past several decades, indium tin oxide (ITO) has been commonly used in the application of transparent conducting electrodes due to its low sheet resistance and high transmittance at the visible region (10–50 ohm·cm−2 at 90% transmittance) [2]. The brittle nature of ITO limits the scope of its practical applications for flexible electronic devices. To replace the conventional ITO electrode in flexible devices, various studies on next-generation FTCEs such as conducting polymer [3], metallic nanowire [4], metal grid [5] and carbon-based materials [6] have been conducted. Further processing is needed to increase the carrier density of graphene

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