Plenarvorträge - DPG-Tagungen

Symposium Organic and Hybrid Systems for Future Electronics Freitag
bonding between thiol end groups and Au electrodes.
For the future electronics, carbon nanotubes are the prime candidates.
Recent progress in the controlled deposition of nanotubes between electrodes
and separation of metallic and semiconducting nanotubes [2] is
reported.
[1] J. Reichert et al., Phys. Rev. Lett. 88, 176804 (2002)
[2] R. Krupke et al., Science 301, 344 (2003)
SYOH 7 Molecular Systems and Applications
Zeit: Freitag 11:15–11:55 Raum: H1
Fachvortrag SYOH 7.1 Fr 11:15 H1
Geometric and electronic structure of sexiphenyl grown
on metal, oxygen modified metal and oxide — •Michael
Ramsey 1 , Georg Koller 1 , Jan Ivanco 1 , Barbara Winter 1 ,
Steve Berkibile 1 , Roland Resel 2 , and Christian Teichert 3 —
1 Experimental Physics, University of Graz, A-8010 Graz, Austria —
2 Solid State Physics,TU-Graz,A-8010,Austria — 3 Physics, University
Leoben,A-8700 Leoben,Austria
For device relevant organic films the organic films crystal structure,
molecular orientation, film morphology and electronic structure are of
prime importance. It will be demonstrated that all these properties can
be drastically affected by the exact nature of the substrate surface on
which they are grown. Here the results of sexiphenyl (6P) growth on
model substrates ranging from clean and oxygen modified single crystal
metal surfaces through to clear conducting oxide surfaces will be discussed.
For growth on Al(111) at room temperature the ordered monolayer
that forms provides the basis for the highly crystalline, single phase,
epitaxial thick 6P that results. Chemisorbed oxygen at the Al surfaces
leads to the formation of 6P films of near vertically oriented molecules. In
contrast oxygen in the Ni(110)-(2x1)O acts as a template for the formation
of strings of azimuthally oriented molecules parallel to the substrate.
On TiO2(110) no wetting layer can be formed and large needle like 6P
crystallites form. The micrometer long needles are oriented exclusively
perpendicular to the atomic rows of the surface while the molecules within
them are parallel them.
SYOH 8 Hybrid Systems
Fachvortrag SYOH 7.2 Fr 11:35 H1
Ambipolar Organic Field-Effect Transistor based on an Organic
Heterostructure — •Constance Rost 1 , David J. Gundlach 2 ,
Siegfried Karg 1 , and Walter Rieß 1 — 1 IBM Research, Zurich
Research Laboratory, CH-8803 Rüschlikon, Switzerland — 2 Laboratory
for Solid State Physics, Department of Physics, ETH Zurich, CH-8093
Zürich, Switzerland
Ambipolar charge injection and transport are a prerequisite for a lightemitting
organic field-effect transistor (LE-OFET). Organic materials,
however, typically show unipolar charge-carrier transport characteristics.
Consequently, organic thin-film field-effect transistors based on a single
material as active layer can typically either be operated as p- or as nchannel
device. We show that by using a heterostructure with pentacene
as hole-transport and Ditridecylperylene-3,4,9,10-tetracarboxylic diimide
(PTCDI-C13H27) as electron-transport material, ambipolar characteristics,
i.e. simultaneous p- and n-channel formation, can be observed in
a single device. An OFET structure is investigated in which electrons
and holes are injected from Mg top and Au bottom contacts into the
PTCDI-C13H27 and pentacene layers, respectively. This device architecture
serves as a model structure for ambipolar field-effect transistors,
which are a prerequisite for light-emitting field-effect transistors.
Zeit: Freitag 12:10–13:10 Raum: H1
Hauptvortrag SYOH 8.1 Fr 12:10 H1
Inorganic Nanorods: Synthesis, Properties, Photovoltaic Applications
— •Delia Milliron, Ilan Gur, and Paul Alivisatos —
University of California, Berkeley, College of Chemistry, Berkeley, CA
94720, USA
Inorganic nanocrystals with well defined shapes are important for understanding
basic size-dependent scaling laws, and may be useful in a
wide range of applications. Methods for controlling the shapes of inorganic
nanocrystals are evolving rapidly. This talk will focus on a strategy
that involves pyrolysis of organometallic precursors in mixtures of hot
organic surfactants. The surfactant mixtures can be used to control the
growth rates of different facets of the nanocrystals, allowing for wide tunability
of shape. This will be illustrated with CdSe and Co nanocrystals.
Both of these materials show pronounced variation of fundamental properties
with aspect ratio. The semiconductor nanorods can be embedded
in plastic films, and they can be aligned in a variety of ways. This talk will
describe recent work on the production of solar cells based on nanoscale
composites of CdSe nanorods and poly-alkyl thiophene semiconductor
polymers, as well as very recent results on the isolation of liquid crystal
phases of semiconductor nanorods. Finally, we will present recent results
on the synthesis of colloidal semiconductor heterostructures with well-
controlled branch points.
Hauptvortrag SYOH 8.2 Fr 12:40 H1
Understanding Donor-Acceptor Photovoltaic Devices — •Neil
Greenham, Baoquan Sun, Henry Snaith, James Barker,
Richard Friend, and Catherine Ramsdale — Cavendish
Laboratory, Madingley Road, Cambridge CB3 0HE, United Kingdom
The power conversion efficiency of a polymer photovoltaic device is determined
by the short-circuit quantum efficiency, the open-circuit voltage
and the shape of the current-voltage curve. A high short-circuit quantum
efficiency requires efficient charge separation and charge collection, and
I will present photovoltaic devices based on conjugated polymers and
CdSe tetrapods which provide efficient charge transport perpendicular
to the plane of the film and which have solar power conversion efficiencies
in excess of 3 processes which determine the open-circuit voltage
in donor-acceptor devices, and will demonstrate the importance of diffusion
currents in generating an additional intensity-dependent open-circuit
voltage. These ideas will be applied to bilayer and blended photovoltaic
devices, where numerical modelling allows the current-voltage curve to
be calculated under illumination.