Plenarvorträge - DPG-Tagungen

Symposium Organic and Hybrid Systems for Future Electronics Donnerstag
carriers in organic solar cells. In this study photoelectron spectroscopy
is applied to determine the electronic properties of the ITO surface. By
treating the ITO substrates with phosphoric or periodic acid these properties
are adjusted to those of the following organic layer. Evidence of adsorbed
acid ions on the electrode surface is found in x-ray photoelectron
spectra. Their inelastic cutoff was determined to calculate work functions.
The work function values are correlated with the performance of
Zn-Phthalocyanine-C60 solar cells. The influence of acid treatments on
the solar cell parameters is compared to the effect of a conventional PE-
DOT:PSS buffer layer.
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High efficiency vacuum deposited solar cells using single or multiple
p-i-n architecture. — •Steffen Grundmann, Jens Drechsel,
Bert Männig, Wenge Guo, Karl Leo, and Martin Pfeiffer
— Insitut für Angewandte Photophysik, TU Dresden, D-01062 Dresden,
Germany
We introduce a p-i-n type heterojunction architecture for organic solar
cells where the active region (i) is sandwiched between two doped widegap
layers (p and n). The photoactive layer is formed by a mixture of
zinc phthalocyanine (ZnPc) and the fullerene C60. In the blend layer, the
ZnPc is found in an amorphous morphology while C60 forms nanocrystallites
of less than 10nm size. The solar cells exhibit an external quantum
efficiency of around 40% between 630nm and 700nm wavelength. With
the help of an optical multilayer model, we optimize the optical properties
of the solar cells by placing the active region at the maximum of the
optical field distribution. The results of the model are largely confirmed
by the experimental findings. For an optically optimized device, we find
an internal quantum efficiency of around 85% at short-circuit conditions.
Adding 10nm thick layer of the red material PTCBI to the active region,
a power conversion efficiency of 2% is obtained. Such optically thin cells
with high internal quantum efficiency are an important step towards high
efficiency tandem cells. First tandem cells, which are not yet optimized,
already show 2.4% power conversion efficiency. Moreover, we present first
promising results on device lifetime under simulated AM 1.5 conditions.
SYOH 5.43 Do 18:00 B
Numerical simulation of photovoltaic devices based on organic
materials — •Fryderyk Kozlowski, Wenge Guo, Bert Maennig,
Jens Drechsel, Martin Pfeiffer, and Karl Leo for the H.
Hope collaboration — Institut für Angewandte Photophysik,01069 Dresden,
Germany
We have modelled the optical and electrical behaviours of organic (pi-n)
and (p-i-i-n) solar cells fabricated in our laboratory by numerical
simulations. In the cells with structure (p-i-n), the dissociation of exitons
and free carrier creation occurrs in a photoactive mixed layer (i) e.g. zinc
phthalocyanine mixed with fullerene (ZnPc:C60). The photovoltaic devices
based on a photoactive donor-acceptor heterojunction with a p-i-i-n
architecture consist of the same organic materials. Here however, exitons
are formed in bulk materials and the dissociation of the excitons takes
place at the interface of neat ZnPc and C60 layers. In the numerical model
describing the electrical properties, we took into account effects like bipolar
charge carrier drift and diffusion, bulk and interface recombination,
trapping, creation, diffusion and quenching of exitons. The distribution
of generated free carriers in the mixed layer or the generation profile of
exitons in heterojunctions, respectively, is calculated from optical simulations.
By including trap-mediated recombination for (p-i-n) solar cells,
we are able to simulate the linear dependence of the short circuit current
on light intensity. Furthermore, we study the optimum thickness of the
active layer and compare it with experimental data. Finally, we show the
temperature dependence of short circuit current and open circuit voltage.
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Photocurrent action spectra and X-ray diffraction on diindenoperylene/pentacene
heterostructures — •D. Kurrle,
S. Hirschmann, and J. Pflaum — III. Physikalisches Institut,
Universität Stuttgart, Germany
As a new candidate for photovoltaic applications, thin films of the
organic semiconductors diindenoperylene (DIP, C32H16) and pentacene
(C22H14) were prepared and examined by measuring the absorption and
photocurrent action spectra.
Samples of different structures were grown by thermal evaporation, using
ITO and silver as electrode materials. DIP/pentacene double layers
as well as co-evaporated mixed layers were studied (both 100-250 nm
in total thickness), both yielding considerable photocurrents up to 50
nA/cm 2 under the applied conditions.
Furthermore, X-ray diffraction and AFM were carried out to obtain
additional information on the structure of the films. The growth of the
DIP/pentacene bilayers showed a pronounced structural dependence on
the substrate temperature (140-400 K) and the underlying electrode material,
whereas the impact on the photocurrent emerged to be minor.
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Optical and Electronic Contributions in Thin Film Organic Solar
Cells — •Helmut Hänsel 1 , Heiko Zettl 1 , Georg Krausch 1 ,
Roman Kisselev 2 , Mukundan Thelakkat 2 , and Hans-Werner
Schmidt 2 — 1 Universität Bayreuth, Physikalische Chemie II —
2 Universität Bayreuth, Makromolekulare Chemie I,D-95447 Bayreuth
We investigate the photocurrent of a (ITO/CuPc/perylene dye/Al)
cell and a (ITO/CuPc/perylene dye/TiO2/Al) cell as a function of the
perylene dye layer thickness. In addition to the experimental data, we
present a model that describes the short circuit current of these cells.
The charge generation probability is estimated from the intensity profile
that is calculated via a matrix transfer algorithm taking into account the
full illumination spectrum. We find that the TiO2 layer modifies the short
circuit current by two effects: Optically, by shifting the charge transfer
interface with respect to the light intensity profile, and electronically, by
introducing a second heterojunction where additional charge transfer can
occur. Thickness dependent studies can clearly separate these two effects
and can yield an estimate of the ratio of the exciton diffusion lengths
in the absorbing media. The high accuracy in thickness variation that is
necessary for such study is achieved by the combinatorial fabrication and
testing of the devices. We can furthermore show that the introduction of
the TiO2 layer leads to a faster and stronger degradation.
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Multilayer solar cells based on polymer nanoparticles —
•Thomas Kietzke 1 , Katharina Landfester 2 , and Dieter
Neher 2 — 1 University of Potdam, Institute of Physics, Am Neuen
Palais 10, D-14469 Potsdam — 2 University of Ulm, Institute of
Macromolecular Chemistry, Albert-Einstein-Allee 11, D-89069 Ulm
Recently, we have demonstrated that polymer nanospheres with diameters
in the range of 30 to 250 nm dispersed in water can be prepared
with the miniemulsion process. First solar cells based on layers of
these nanoparticles have shown efficiencies comparable to solvent processed
layers. Formation of films from polymer nanoparticles opens up
new strategies for the deposition of multilayer assemblies, since the semiconducting
polymer nanospheres are dispersed in water. Preparing multilayer
structures of polymers from organic solvents is often difficult if the
polymers of e.g. the second layer is deposited from a solvent, which is also
a good solvent for the underlying polymer. Utilizing dispersions of polymer
nanospheres can help to circumvent this problem. After preparing the
first nanoparticle layer, the sample is thoroughly dried to completely remove
residual water. Then, a second nanosphere layer is deposited on top,
resulting in a multilayer assembly with a well-defined polymer-polymer
interface and no interdiffusion of the polymers in the separate layers. We
show the results on double layer polymer solar cells with ITO and Ca
electrodes as well as devices including a thin TiO2 electron-accepting
layer. Reference: [1] T.Kietzke, D. Neher et. al. Nature Materials, June
2003, 408-412
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Organic Photovoltaic Elements - Influence of 100 nm scale
electrode spacing on morphology and efficiency for PF/PANI
conjugated block copolymer — •Jörg Seekamp 1 , R. Güntner 2 ,
V.G. Solovyev 1 , A.P. Kam 1 , A. Goldschmidt 1 , T. Farrell 2 , U.
Scherf 2 , and C.M. Sotomayor Torres 1 — 1 Institute of Materials
Science and Department of Electrical and Information Engineering, University
of Wuppertal, Gauß Straße 20, 42097 Wuppertal, Germany —
2 Fachbereich Chemie, Makromolekulare Chemie, University of Wuppertal,
Gauß Straße 20, 42097 Wuppertal, Germany
The transport properties of organic semiconductors in solar cells are
the object of intense research. The efficiency of these devices crucially
depends on the charge separation and effective transport to metal electrodes.
This work combines closely spaced electrodes and the intrinsically
nanostructured morphology of a block copolymer to improve the
efficiency. The idea is to direct the intrinsic nanostructuring along the