Abstract
To implement large-area solution-processed graphene films in low-cost transparent conductor applications, it is necessary to have the control over the work function (WF) of the film. In this study we demonstrate a straightforward single-step chemical approach for modulating the work function of graphene films. In our approach, chemical doping of the film is introduced at the moment of its formation. The films are self-assembled from liquid-phase exfoliated few-layer graphene sheet dispersions by Langmuir-Blodgett technique at the water-air interfaces. To achieve a single-step chemical doping, metal standard solutions are introduced instead of water. Li standard solutions (LiCl, LiNO3, Li2CO3) were used as n-dopant, and gold standard solution, H(AuCl4), as p-dopant. Li based salts decrease the work function, while Au based salts increase the work function of the entire film. The maximal doping in both directions yields a significant range of around 0.7 eV for the work function modulation. In all cases when Li-based salts are introduced, electrical properties of the film deteriorate. Further, lithium nitrate (LiNO3) was selected as the best choice for n-type doping since it provides the largest work function modulation (by 400 meV), and the least influence on the electrical properties of the film.
Highlights
Graphene, consisting of a single layer carbon arranged in a hexagonal lattice, has attracted extensive interest because of the excellent mechanical and electrical properties associated with its two dimensional structure[1,2,3,4]
We systematically investigated single-step work function modulation of the liquid-phase exfoliation (LPE) graphene sheets (GSs) films achieved by chemical doping
Single-step work function modulation means doping of the film at the moment of its formation from the LPE graphene dispersion by Langmuir-Blodgett assembly (LBA) technique at the air-metal standard solution interface
Summary
Graphene, consisting of a single layer carbon arranged in a hexagonal lattice, has attracted extensive interest because of the excellent mechanical and electrical properties associated with its two dimensional structure[1,2,3,4]. In order to access the full potential of LPE-processed graphene, thin-films needs to be controllably fabricated utilizing techniques capable to introduce self-ordering of GSs7 One such example is Langmuir-Blodgett assembly (LBA). The chemical doping has been reported to be an effective method for doping of CVD graphene and tuning its work function by charge transfer between the graphene sheet and metal salts, organic dopants, or metal oxide layers[12,14,21,22,23,24,25,26,27,28]. Single-step work function modulation means doping of the film at the moment of its formation from the LPE graphene dispersion by LBA technique at the air-metal standard solution interface. We have demonstrated tunability of the WF in the range of almost 1 eV, making these metal-salt treated LPE-based graphene electrodes suitable candidates for both electron and hole injection interfaces
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