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Issue 3, 2017
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Solution-processed 2-dimensional hole-doped ionic graphene compounds

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Contacts with suitable work functions are important not only for ohmic injection of carriers but also to set up the built-in potential required for various semiconductor processes including current rectification, light emission and photovoltaic generation. For two-dimensional (2D) materials, one way to shift the work function is by intercalation doping with suitable donors or acceptors. Here, using an atomic sheet transfer methodology, we report layer-by-layer assembly of centimeter-square sizes of graphene–fluorofullerene multilayers through directed stacking of chemical-vapor-deposited (CVD) graphene sheets and self-assembly of fluorofullerene acceptors, for example C60F48, to give a 1 eV increase in work function to 5.7 eV, which is unprecedented for a well-defined compound. These assemblies exhibit an unusual motif of fully-ionized large dopants in open packing with the graphene sheets. As a consequence, they show a sizeable electrostatic dipole to give ultrahigh work function at acceptor-terminated surfaces even for a moderate hole doping level of 1.6 × 1013 cm−2 per sheet. They exhibit little additional carrier scattering and a remarkable chemical stability. Hall measurements reveal unity doping efficiency with temperature-independent hole density, mobility and electrical conductivity down to 2.5 K, which are atypical of conventional graphite intercalation compounds. These materials provide the first examples of a novel domain of doped 2D assemblies where large ions are incorporated through room-temperature solution processing, which opens new opportunities beyond van der Waals semiconductor heterostructures.

Graphical abstract: Solution-processed 2-dimensional hole-doped ionic graphene compounds

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Article information

06 feb. 2017
24 mar. 2017
First published
24 mar. 2017

Mater. Horiz., 2017,4, 456-463
Article type

Solution-processed 2-dimensional hole-doped ionic graphene compounds

F. Kam, R. Png, M. C. Y. Ang, P. Kumar, K. Rubi, R. Mahendiran, O. Solomeshch, N. Tessler, G. Lim, L. Chua and P. K. H. Ho, Mater. Horiz., 2017, 4, 456
DOI: 10.1039/C7MH00068E

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