jp5b11535_si_001.pdf (802.29 kB)
Impacts of Molecular Orientation on the Hole Injection Barrier Reduction: CuPc/HAT-CN/Graphene
journal contribution
posted on 2016-02-04, 15:10 authored by Junkyeong Jeong, Soohyung Park, Seong
Jun Kang, Hyunbok Lee, Yeonjin YiThe molecular orientation affected
by the interaction between a
substrate and deposited molecules plays an important role in device
performance. It is known that the molecular orientation influences
not only the charge transport property but also its electronic structure.
Therefore, the combined study of morphology and electronic structure
is of high importance for device application. As a transparent electrode,
graphene has many promising advantages. However, graphene itself does
not have an adequate work function for either an anode or a cathode,
and thus the insertion of a charge injection layer is necessary for
it to be used as an electrode. In this study, the hole injection barrier
(HIB) reduction was investigated at the interface of copper phthalocyanine
(CuPc)/graphene with the insertion of a hexaazatriphenylene
hexacarbonitrile (HAT-CN) layer between them. The insertion
of the HAT-CN layer roughens the originally flat graphene surface
and it weakens the π-interaction between CuPc and of graphene.
This induces face-on and edge-on mixed orientations of CuPc, while
CuPc on bare graphene shows merely a face-on orientation. As a result,
the HIB is reduced by the contribution of edge-on CuPc having lower
ionization energy (0.37 eV) along with the high work function of the
HAT-CN layer (0.26 eV).