Plenarvorträge - DPG-Tagungen

Symposium Organic and Hybrid Systems for Future Electronics Donnerstag
SYOH 5.35 Do 18:00 B
Energy Shifts in Copper Phthalocyanine Grown on Hydrogen
Passivated Si(111) — •M. Gorgoi, T. U. Kampen, and D. R. T.
Zahn — Insitut f”ur Physik, TU Chemnitz, 09107 Chemnitz, Germany
Being a major component in organic light emitting devices and solar
cells, copper phthalocyanine (CuPc) owes its increasingly attractive application
potential to its optical and electronic properties. In this contribution
ultraviolet photoemission spectroscopy (UPS) and inverse photoemission
spectroscopy (IPES) were employed to study the electronic density
of states of CuPc layers deposited onto hydrogen passivated Si(111)
substrates as a function of film thickness. The highest occupied molecular
orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)
features are found to shift gradually in the same direction with increasing
film thickness. HOMO and LUMO shift away from and towards the
Fermi level, respectively. Saturation occurs at approximately 10 nm coverage,
when the shifts amount to about 0.4 eV. In spite of this shift, the
HOMO – LUMO peak to peak difference is found to be constant at (2.95
– 0.25) eV in agreement to previous studies [1]. The 0.4 eV shifts of the
HOMO and LUMO are proposed to originate from the growth morphology
of CuPc. [1] I.G.Hill, A. Kahn, Z.G. Soos, R.A. Pascal, Jr., Chem.
Phys. Lett. 327, 181, (2000)
SYOH 5.36 Do 18:00 B
Electrical Properties of a Hybrid Ag / DiMe-PTCDI / GaAs
(100) device — •Henry Mendez, Ilja Thurzo, Thorsten Kampen,
and Dietrich R.T. Zahn — Institut für Physik, Technische Universität
Chemnitz
The perylene derivative dimethyl-3,4,9,10-perylenetetracarboxylic diimide
(DiMe-PTCDI) was used for the organic modification of Ag Schottky
contacts on n-type GaAs(100) surfaces. The transport electronic
properties were investigated recording in situ current-voltage (IV) and
capacitance-voltage (CV) characteristics, as well as ex situ characterisation
by Deep Level Transient Spectroscopy (DLTS). Additionally, an
examination of the unoccupied states of DiMe-PTCDI / GaAs(100) interface
was performed by Ultraviolet Photoemission Spectroscopy (UPS).
Modification of the Schottky diodes was obtained by growing an organic
DiMe-PTCDI layer on GaAs(100) prior to the preparation of silver
dots. Examination of the in situ IV characteristics of the organic modified
Schottky contacts shows a decrease in effective barrier height as a
function of organic film thickness. This suggests that the transport level
band in the organic DiMe-PTCDI layer, lies below the conduction band
minimum of GaAs(100). The transport level in the organic layer is further
evaluated by DLTS measurements. With UPS an energy level alignment
for the GaAs(100) / DiMe-PTCDI / Ag interface is deduced.
SYOH 5.37 Do 18:00 B
Interface Formation Between Mg and DiMe-PTCDI Studied
by Raman Spectroscopy — •Beynor Antonio Paez Sierra, Georgeta
Salvan, Reinhard Scholz, Thorsten U. Kampen und
Dietrich R. T. Zahn — Institut für Physik, Technische Universität
Chemnitz, 09107, Germany
The metal / organic interface plays an important role in the performance
of devices with organic active layers. In particular the N,N ′ -DiMethyl-
3,4,9,10-Perylene Tetra Carboxylic DiImide (DiMe-PTCDI) is a promising
candidate in organic field effect transistors. Previous studies revealed
that the interaction of Ag and In with DiMe-PTCDI is weak [1].
In this work the interface formation between Mg and DiMe-PTCDI
films with different thicknesses grown on S-passivated GaAs (100) substrates
is investigated in situ by Raman spectroscopy. When Mg is deposited
onto a 15 nm DiMePTCDI film the external molecular modes
are preserved even up to 15 nm Mg coverage, indicates a low diffusion
of Mg into the DiMePTCDI film. Concerning the internal molecular modes,
the Mg deposition induces a break down of selection rules reflecting
a dynamical charge transfer between the DiMe-PTCDI molecules and the
metal. This is in contrast to the Mg / PTCDA interface where strong
reaction was observed.
[1] B.A. Paez, G. Salvan, R. Scholz, T. U. Kampen, and D.R.T. Zahn,
SPIE USE, V 1 5217-13, (2003).
SYOH 5.38 Do 18:00 B
Chemistry and Electronic Properties of Mg/PTCDA Interface
— •G. Gavrila 1 , H. Mendez 1 , T. Kampen 1 , D. Vyalikh 2 , W.
Braun 2 , and D.R.T Zahn 1 — 1 Institut für Physik, TU Chemnitz,
09107 Chemnitz, Germany — 2 BESSY GmbH, 12489 Berlin, Germany
The chemical and electronic properties of interfaces formed between
an organic semiconductor, i.e. 3,4,9,10-perylene-tetracarboxylic dianhydride
(PTCDA), and the low electron affinity metal Mg were investigated
using Near Edge X-ray Absorption Fine Structure (NEXAFS) and PhotoEmission
Spectroscopy (PES). NEXAFS spectra taken for C K-edge
and O K-edge of PTCDA show that the intensity in the π*-resonance
decreases after deposition of Mg. This is interpreted as a partial occupation
of the lowest unoccupied molecular orbital. Since Mg possesses a
smaller electronegativity than PTCDA, a negative charge transfer from
Mg to PTCDA can be expected. Changes in C1s and O1s core levels and
the valence band structures corroborate this interpretation. Moreover,
changes in the C=O component of core levels indicate a strong chemical
reaction of Mg with the organic material. Previous work based on
Raman Spectroscopy and NEXAFS revealed considerable differences between
Mg/PTCDA and Ag/PTCDA interfaces. Here, it was found that
the Ag atoms do not disrupt the chemical structure of the PTCDA and
do not diffuse into the organic film.
SYOH 5.39 Do 18:00 B
Organic pn-homojunction using a new class of organic donors —
•K. Harada 1 , A.G. Werner 1 , M. Pfeiffer 1 , K. Leo 1 , C. Bloom 2 ,
and C.M. Elliott 2 — 1 Institut für Angewandte Photophysik, TU Dresden,
D-01062 Dresden — 2 Dep. of Chemistry, Colorado State University,
Fort Collins, CO 80523
Organic devices with p-type doped hole transport layers are now well
established. So far, n-type doped electron transport materials have been
realized with alkali metals as dopants only, because the common matrices
are rather weak electron acceptors. This demands for donor compounds
with a very low ionization potential, which are generally difficult to handle.
This limitation seemingly prevented n-type doping using very strong
organic donors.
We present a study of n-type doping of phthalocyanine zinc (ZnPc)
using metalorganic complexes as donors. ZnPc is generally considered as
a p-type semiconductor. However, using the transition metal complexes
as donors, we are able to achieve n-type conduction in this material. Conductivies
in the order of 10 −6 S/cm are observed and the conduction type
was confirmed by field effect measurements.
This enabled us to realize the first stable organic p-n junctions constisting
of p- and n-type doped layers of the same material (homo-junctions).
They have very high built-in potentials. This does not only reflect the
versatility of doping in organic devices, but pave a way to increase the
open circuit voltage of organic solar cells and to use n-type doped electron
transport layers in OLEDs.
SYOH 5.40 Do 18:00 B
Leuco bases as dopants for n-type doping of organic thin films
— •Fenghong Li, Ansgar Werner, Martin Pfeiffer und Karl
Leo — Institut fuer Angewandte Photophysik, TU Dresden, 01062
Doping of organic thin films by insertion of electron donating (n dopant)
or electron accepting (p dopant) atoms or moleculars has been
shown to be efficient and to increase film conductivity by several orders
of magnitude. N-type doping of electron transport materials with alkali
metal atoms has also been extensively reported, but these metals may
not be suitable for controlled doping. Now, organic molecules as dopants
for n-type doping are also investigated for device applications.
We demonstrated that the cationic dye pyronin B (pyB) greatly increased
the conductivity of electron transporting materials /1/. Based on
this finding, we further studied other triphenylmethane dyes as dopants
for fullerene C60 used in solar cells. For instance, conductivities up to
7.9·10 −3 S/cm were achieved when C60 was doped with Crystal Violet.
Such high conductivities render the ohmic losses in the electron transport
layers of organic solar cells neglectable.
As in the case of pyronin B, the leuco bases of the corresponding dyes
are formed by during sublimation. We found that these leuco bases become
re-oxidized to the cation in the layer by electron transfer to electron
accepting matrices, leading to the doping effect.
/1/ A.G. Werner, F. Li et al Appl. Phys. Lett., 82, 4495
SYOH 5.41 Do 18:00 B
A photoelectron spectroscopy study of transparent electrodes
in organic solar cells — •Mirko Vogel, Boyan Johnev, and
Konstantinos Fostiropoulos — Hahn-Meitner-Institut Berlin,
Glienicker Str. 100, 14109 Berlin
The interface of indium-tin oxide (ITO) electrodes with organic layers
has been shown to play an important role for the collection of charge