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@PHDTHESIS{Hpkes:55223,
author = {Hüpkes, Jürgen},
title = {{U}ntersuchung des reaktiven {S}putterprozesses zur
{H}erstellung von aluminiumdotierten {Z}inkoxid-{S}chichten
für {S}ilizium-{D}ünnschichtsolarzellen},
volume = {52},
school = {RWTH Aachen},
type = {Dr. (Univ.)},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
reportid = {PreJuSER-55223},
isbn = {3-89336-435-8},
series = {Schriften des Forschungszentrums Jülich. Reihe
Energietechnik / Energy Technology},
pages = {X, 170 S.},
year = {2006},
note = {Record converted from VDB: 12.11.2012; RWTH Aachen, Diss.,
2005},
abstract = {This thesis addresses the development of aluminum doped
zinc oxide (ZnO:Al) films by reactive sputter deposition.
The study focuses on the relation between deposition
conditions and the resulting electrical, optical and
structural film properties. The structure of the ZnO:Al
films strongly affects the surface morphology obtained after
wet chemical etching. The technological goal was the design
of ZnO:Al films with optimized surface texture and thus
light scattering properties for the application as front
contact in amorphous (a-Si:H) and microcrystalline (μc-
Si:H) based thin film solar cells. The comparatively low
absorption coefficient of silicon in the long wavelength
range of the sun spectrum necessitates additional mechanisms
to enhance light absorption within the silicon layers. This
can be realized by a combination of rough, light scattering
front contacts and highly-reflective rear contacts.
Initially smooth, sputter deposited ZnO:Al films can be
roughened by post-deposition wet-chemical etching. In the
ideal case, these rough layers introduce almost completely
diffuse transmission, and back reflector and front contact
guide the light through the silicon layers until it is
totally absorbed (ideal light trapping). The ZnO:Al films
were prepared by reactive mid-frequency (MF) sputtering from
metallic Zn:Al targets in a vertical in-line deposition
system. Initially, technological aspects like stabilization
of the working point and the influence of substrate movement
required for dynamic deposition were studied. Doping
concentration and deposition conditions were varied to
optimize the optical and electrical ZnO:Al properties,
leading to resistivities ρ < 3 · 10$^{−4}$ Ωcm and at
the same time transmission values exceeding 80 \% in the
visible and near infrared spectrum. By increasing deposition
pressure, decreasing substrate temperature or shifting the
working point towards the oxide mode, the surface morphology
after etching in diluted hydrochloric acid could be changed
from crater-like to granular shapes. The working point
during reactive sputtering enables the density of points of
etch attack in post-deposition etching steps to be varied
over a wide range. In subsequent discussion concerning the
etching behavior of sputter deposited ZnO:Al films in acids
and bases, known dependencies are identified and some
analogies to the etching of ZnO single crystals are drawn.
Based on the experimental findings we developed an optimized
high rate deposition process including post-deposition
etching for surface textured ZnO:Al films. When applied as a
front contact in solar cells, initial efficiencies of 9.9 \%
and 8.2 \% were realized for single junction cells with
a-Si:H and μc-Si:H absorber layers, respectively. These
ZnO:Al front contacts were sputtered at dynamic deposition
rates of 100 nm·m/min which correspond to static deposition
rates as high as 400 nm/min. For an a-Si:H/μc-Si:H tandem
structure solar module, an initial aperture area efficiency
of 9.7 \% was obtained on 64 cm$^{2}$ aperture area.},
cin = {IPV},
ddc = {620},
cid = {I:(DE-Juel1)VDB46},
pnm = {Erneuerbare Energien},
pid = {G:(DE-Juel1)FUEK401},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
url = {https://juser.fz-juelich.de/record/55223},
}