Versatile and Tunable Electrical Properties of Doped Non-oxidized Graphene using Alkali Metal Chloride.

With the emergence of wearable and flexible electronics, graphene has recently been developed for transparent electrodes in field effect transistors, light-emitting diodes, and organic photovoltaic cells. Graphene doping methods can decrease sheet resistance and modulate work function while retaining high transparency, for transparent conductive electrodes (TCEs). In this work, a chemical doping method, which incorporates metal chlorides (NaCl, KCl and AuCl3) and organic compounds (HNO3) as chemical dopants, was used to control the charge carrier density, band gap and work function, without damage to the carbon network. Furthermore, we synthesized non-oxidized graphene with large lateral sizes of more than 5 μm using ternary graphite intercalation compounds (t-GICs). The resulting graphene flake films (DGFFs) doped with AuCl3 exhibited the lowest reported sheet resistance (2.008 X 105 S/m at ~75% transmission), to the best of our knowledge, and controlled the work function from 4.32 eV to 5.1 eV. Doping with interfacial dipole complexes of metal cations with low work function, and reactive radicals like -OH were also considered for tuning sheet resistance and work function. An organic photovoltaic device (OPV) using Au-DGFFs as a hole transporting layer (HTL) demonstrated enhanced power conversion efficiency (PCE) while maintaining high optical transparency in visible light. This approach to forming transparent conducting electrodes is expected to open numerous potential DGFFs applications.