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@PHDTHESIS{Schrder:565927,
author = {Schröder, Sonja},
othercontributors = {Kumpf, Christian and Gottfried, Michael},
title = {{S}tructural and electronic characterization of
hetero-organic {NTCDA}-{C}u{P}c adsorbate systems on
{A}g(111)},
school = {RWTH Aachen},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2016-00216},
pages = {1 Online-Ressource (154 Seiten) : Illustrationen,
Diagramme},
year = {2016},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen, 2015},
abstract = {Organic solar cells have many advantages compared to
inorganic devices e.g. lower costs, thinner active layers
and easier production, but to compete with the inorganic
solar cells their efficiency has to be increased. Different
acceptor-donor systems therefore have to be studied as it is
known that charge transport depends on molecular geometry of
the unit cell. In this work a systematic study of laterally
and vertically mixed structures of the charge acceptor
1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) and
the donor copper-II-phthalocyanine (CuPc) adsorbed on
Ag(111) is presented.Laterally mixed layers were studied,
where the unit cell size and shape can be tuned by using
different stoichiometric ratios of both molecules. NTCDA and
CuPc form five coverage dependent mixed structures on
Ag(111) with (uni-axial) commensurate substrate relations,
which have surprisingly large unit cells, compared to
PTCDA-CuPc heteromolecular systems. An adsorption height
alignment of the molecules was found for a CuPc-rich and a
NTCDA-rich phase, as was earlier observed for PTCDA and CuPc
by Stadtmüller et al. The molecules are however adsorbed at
lower heights compared to their homomolecular structures in
the NTCDA-rich phase. Differences in the contrast of the
NTCDA molecules in STM images indicate that the NTCDAs are
located at different adsorption heights. The study of the
electronic properties by ARPES and STS showed that the
lowest unoccupied molecular orbital (LUMO) of NTCDA is more
populated than in the homomolecular structure and the LUMO
of CuPc is empty. This confirms the model of charge
reorganization of Stadtmüller et al., who claimed that the
electrons are transferred from the donor (CuPc) via the
substrate to the charge acceptor (PTCDA). Our measurements
proved that NTCDA is able to take up the whole charge
offered by CuPc, although it is a weaker charge acceptor
than PTCDA.The investigation of three differently stacked
NTCDA-CuPc systems, CuPc molecules on top of a relaxed (RML)
and a compressed monolayer (CML) of NTCDA and NTCDA on a
monolayer of CuPc on Ag(111), allowed for the study of the
interaction between the organic layers. Molecular exchange
was observed for CuPc on the RML of NTCDA and for NTCDA on a
ML of CuPc. The CuPc molecules have sufficient space to
adsorb between the NTCDAs of the RML. The 10 $\%$ higher
packing density of the CML compared to the RML however
prevents the CuPc molecules from diffusing into the first
layer. Furthermore the CuPc molecules on the compressed ML
of NTCDA preferentially align on the high symmetry
directions of the substrate. ARPES measurements proved that
the CuPcs in the second layer lead to a stronger bonding of
the NTCDA molecules to the substrate, but charge transfer to
the second layer can be excluded.},
cin = {139320 / 130000},
ddc = {530},
cid = {$I:(DE-82)139320_20140620$ / $I:(DE-82)130000_20140620$},
typ = {PUB:(DE-HGF)11},
urn = {urn:nbn:de:hbz:82-rwth-2016-002166},
url = {https://publications.rwth-aachen.de/record/565927},
}
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