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@PHDTHESIS{Michard:202665,
author = {Michard, Stephan},
title = {{R}elation between growth rate, material quality, and
device grade condition for intrinsic microcrystalline
silicon: {F}rom layer investigation to the application to
thin-film tandem solar cells},
volume = {259},
school = {RWTH Aachen},
type = {Dr.},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
reportid = {FZJ-2015-04855},
isbn = {978-3-95806-048-7},
series = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
Umwelt / Energy $\&$ Environment},
pages = {vi, 184 S.},
year = {2015},
note = {RWTH Aachen, Diss., 2015},
abstract = {Investigations on the relation between the growth rate,
material quality, and device grade condition for intrinsic
microcrystalline silicon is presented in this thesis.
Hydrogenated microcrystalline silicon deposited by plasma
enhanced chemical vapor deposition is a widely used material
for the absorber layer of the bottom solar cell in silicon
thin-film tandem solar cells. Microcrystalline silicon is a
mixed phase material consisting of crystal grains, amorphous
phase, grain boundaries, and voids. To guarantee sufficient
light absorption absorber layer thicknesses of more than 1
μm to 3 μm are required for the absorber layer of the
bottom solar cell. The increase of the deposition rate for
intrinsic microcrystalline silicon is one essential point
for cost reduction in the mass production of thin-film solar
cells. The combination of excitation frequencies in the very
high frequency range altogether with the application of the
high pressure depletion regime enabled to reach deposition
rates up to 2.8 nm/s for optimal phase mixture material,
which is until today considered to be of device grade
quality. According to conductivity, electron spin resonance,
and Raman measurements the quality properties of the
material deposited at high deposition rates is similar to
reference material deposited at low deposition rates.
Nevertheless this material showed to be susceptible to
oxygen uptake, which was shown to occur along the grain
boundaries. Furthermore a decrease in crystal grain size
with a simultaneous increase in tensile stress was observed
by X-ray diffraction and Raman measurements, respectively.
Thickness dependent Raman measurements showed a decrease in
incubation layer thickness with increasing deposition rate.
The investigations performed by X-ray diffraction and
thickness dependent Raman measurements were supported by
investigations performed with transmission electron
microscopy. With this work it was found that the present
criteria to classify microcrystalline silicon being of
device grade quality should be extended for deposition rates
beyond 1nm/s. In addition to the measures describing the
optimal phase mixture quantities describing the materials
microstructure, the tendency for oxygen uptake, and the
mechanical stress should be taken into account. The device
performance of microcrystalline thin-film single junction as
well as of amorphous / microcrystalline thin-film tandem
solar was observed to decrease with increasing deposition
rate. The decrease in device performance was shown to be
either related to inferior material quality of the
microcrystalline absorber layer with increasing deposition
rate and to an impairment of the pi-interface of the
microcrystalline (sub) solar cell. Simulations on the impact
of ions in matter showed that a damage of the pi-interface
by ion bombardment is unlikely. As possible sources for the
impairment ofthe pi-interface a variation of the nucleation
conditions and structural inhomogeneities at the
substrate/film interface are discussed. Despite the decrease
in device performance of the amorphous / microcrystalline
thin-film tandem solar cells calculations showed that the
output of deposition systems in produced Watt per hour can
be increased by more than a factor of two. An increase in
system output leads to a decrease in costs per produced unit
and can lead to a decrease in initial investment costs.},
cin = {IEK-5},
cid = {I:(DE-Juel1)IEK-5-20101013},
pnm = {121 - Solar cells of the next generation (POF3-121)},
pid = {G:(DE-HGF)POF3-121},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
url = {https://juser.fz-juelich.de/record/202665},
}