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@PHDTHESIS{Richter:722212,
author = {Richter, Alexei},
othercontributors = {Rau, Uwe and Knoch, Joachim},
title = {{N}anocrystalline silicon oxide in silicon heterojunction
solar cells},
volume = {416},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
reportid = {RWTH-2018-223448},
isbn = {978-3-95806-310-5},
series = {Schriften des Forschungszentrums Jülich: Reihe Energie
$\&$ Umwelt / Energy $\&$ Environment},
pages = {1 Online-Ressource (166 Seiten) : Illustrationen},
year = {2018},
note = {Druckausgabe: 2018. - Onlineausgabe: 2018. - Auch
veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 2018},
abstract = {In the recent decade world record solar energy conversion
efficiencies have been achieved by the silicon
heterojunction (SHJ) solar cell technology. However, the
parasitic absorption within the doped amorphous silicon
(a-Si:H) layers still causes a significant reduction in the
short circuit current density of a SHJ solar cell. In
contrast, thin films of nanocrystalline silicon oxide
(nc-SiOx:H) are significantly more transparent. Therefore,
the aim of this thesis was to develop doped nc-SiOx:H films
at an increased deposition frequency to improve the
optoelectronic trade-off of the films and apply these layers
in SHJ solar cells to achieve a low parasitic absorption
and, thereby, an enhanced short circuit current density. In
this work films of nc-SiOx:H were developed at 81.4 MHz
using plasma enhanced chemical vapor deposition. By
exploiting the increased atomic H density at 81.4 MHz, an
improved phase separation was achieved in comparison to
films deposited at 13.56 MHz within the same deposition
system. Within these variations four distinct regions of
nc-SiOx:H deposition were identified according to their
microstructure and their properties. In particular these
are: a region of amorphous growth (“fully amorphous
region”), a region with low amounts of the nc-Si phase and
the a-SiOx:H phase (“onset of nc-Si formation”),
nc-SiOx:H films of high nc-Si and a-SiOx:H phase contents
(“O and nc-Si enrichment”), and a region with a
preferential incorporation of a-SiOx:H against nc-Si
(“nc-Si deterioration”). Particularly, films deposited
at the transition between the “O and nc-Si enrichment”
and the “nc-Si deterioration” region exhibited a high
optoelectronic performance. A detailed investigation of the
microstructure via atom probe tomography revealed the
intricate three-dimensional structure of the nc-Si network
and indicated a nearly homogeneous distribution of the
dopant atoms across all phases in contrast to thermally
produced nc-Si in SiO2.After the material development, the
nc-SiOx:H layers were applied in SHJ solar cells. Starting
with planar substrates passivated by intrinsic a-SiOx:H
layers, n-type nc-SiOx:H front-emitter layers led to an
increase in the short circuit current density of the solar
cells with an increasing a-SiOx:H content in the nc-SiOx:H
layers. At the same time, highly transparent nc-SiOx:H
layers severely limited the fill factor of the solar cells.
These investigations were accompanied by optical simulations
using OPAL 2. Additionally, a significant enhancement of the
open circuit voltage was achieved by substituting the
intrinsic a-SiOx:H by intrinsic a-Si:H due to the superior
surface passivation of c-Si by the annealed a-Si:H layers.
Furthermore, nano-imprint lithography was employed to
produce Si random pyramid textured SiO2-like anti-reflection
coatings on planar SHJ solar cells, which enhanced the light
incoupling and resulted in an increase of the short circuit
current density. The combination of an increased light
incoupling and increased light trapping was achieved by Si
random pyramid textured Si substrates. Here, the surface
passivation of the absorber by intrinsic a-Si:H was
confirmed to be comparable to the planar absorbers by
considering the effect of the increased surface area and the
absorber thickness. In total, a gradual enhancement of the
solar energy conversion efficiency from 19 to $21.4\%$ was
accomplished in the course of this work for the SHJ solar
cells.},
cin = {615610 / 616210},
ddc = {621.3},
cid = {$I:(DE-82)615610_20140620$ / $I:(DE-82)616210_20140620$},
typ = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2018-223448},
url = {https://publications.rwth-aachen.de/record/722212},
}
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