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@PHDTHESIS{Qiu:973466,
author = {Qiu, Depeng},
othercontributors = {Rau, Uwe and Vescan, Andrei},
title = {{D}evelopment of industry-scalable processes for
nanocrystalline silicon oxide in silicon heterojunction
solar cells},
volume = {619},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH, Zentralbibliothek, Verlag},
reportid = {RWTH-2023-10814},
series = {Schriften des Forschungszentrums Jülich. Reihe Energie
$\&$ Umwelt = Energy $\&$ environment},
pages = {1 Online-Ressource (202 Seiten) : Illustrationen,
Diagramme},
year = {2023},
note = {Druckausgabe: 2023. - Onlineausgabe: 2023. - Auch
veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2024; Dissertation, RWTH Aachen University, 2023},
abstract = {Thanks to the excellent passivation of hydrogenated
amorphous silicon (a-Si:H) to wafer surface, high open
circuit voltage (Voc) as well as power conversion efficiency
(η) have been achieved by the silicon heterojunction (SHJ)
solar cell technology in the recent decades. However, a
significant parasitic absorption in doped a-Si:H re- sults
in a low short circuit current density (Jsc), limiting the
cell performance of SHJ solar cells. Doped hydrogenated
nanocrystalline silicon oxide (nc-SiOx:H), consisting of
conductive silicon crystallites (nc-Si:H) embedded in
transparent hydrogenated amorphous silicon oxide (a-SiOx:H)
matrix, is an attractive alternative material to the
commonly used a-Si:H in SHJ solar cells to further improve
the cell performance. A trade-off between the optical and
the electrical properties always need to be taken into
account when applying the nc-SiOx:H(n) films in SHJ solar
cells. The goal of this thesis is to systematically
investigate the implementation of nc-SiOx:H(n) in SHJ solar
cells, to find the correlation between the material
properties and the de- vice performance, and to demonstrate
the industrial applicability of nc-SiOx:H in SHJ solar
cells.In the first part of this work, n-type nc-SiOx:H and
hydrogenated nanocrys- talline silicon (nc-Si:H) (x equals
zero) layers were developed and compared in an industrial
multi-substrate plasma enhanced chemical vapor deposition
(PECVD) system for the application in full-sized (>156×156
mm2) SHJ solar cells. By means of optical, electrical and
structural material characterizations, the influence of de-
position parameters, such as deposition power density (P ),
deposition pressure (p) and gas compositions, was
investigated. It was found that the response of nc-SiOx:H to
the variation of deposition parameters is different from
that of nc-Si:H layers. Moreover, a synergistic effect of
CO2 and PH3 or SiH4 on the material properties of nc-SiOx:H
films was observed. To acquire the nc-SiOx:H films with
high transparency and sufficient conductivity, high volume
fraction of a-SiOx:H (Fa-SiO2 ) and nc-Si:H (Fc), but low
a-Si:H volume fraction (Fa-Si:H) are required. Furthermore,
a very good homogeneity of the nc-SiOx:H(n) films prepared
in this large-area system was demonstrated.In the second
part of this work, the nc-SiOx:H layers at thickness of 15
nm were integrated in the rear-junction SHJ solar cells as
electron transport layer (ETL) on n-type quarter-M2-sized
c-Si wafers. It was demonstrated that the variation of
material properties of nc-SiOx:H(n) does not affect the Voc
but has a big influence on the Jsc and the fill factor (FF
) of SHJ solar cells as well as the contact resistivity
(ρc) of indium tin oxide (ITO) / nc-SiOx:H(n). It was found
that the ρc of ITO / nc-SiOx:H(n) can be reduced by
increasing the dark conductivity (σ) and the Fc, or
reducing the optical band gap (E04) of nc-SiOx:H(n). In
total, the best performed cell in the preliminary
development shows Voc of 728 mV, FF of $76.7\%,$ Jsc of 39.1
mA/cm2 and η of $21.83\%.$ To have a comprehensive
knowledge on efficiency limit of the solar cell, a highly
predictive model was built in Quokk3 simulator and a power
loss analysis was carried out. It was found that the
bottleneck to the cell performance is the properties of the
front layer stacks. Then, a road map to $24\%$ of power
conversion efficiency was put forward.In the third part of
this work, a systematical optimization has been done to
improve the cell performance. The solar cells with
different ETL structure at various thickness were
fabricated. Significantly deteriorated contact property of
nc-SiOx:H(n) / ITO was observed when reducing the nc-SiOx:H
thickness from 20 to 5 nm, which can not be compensated by
the decreased parasitic absorption on the front. By
inserting the a-Si:H(n) or the highly conductive nc-Si:H(n)
between nc-SiOx:H(n) and ITO an enhancement of the contact
property can be achieved. Besides, it was demonstrated that
a rapid nucleation and a thinner incubation layer can be
obtained by depositing nc-Si:H(n) seed layer prior to the
nc-SiOx:H(n). Com- pared to the cells with nc-SiOx:H(n)
single layer, around $3\%$ relative gain of η is achieved
for the cells with nc-Si:H(n) / nc-SiOx:H(n) multi-layer. To
enhance the surface passivation, the hydrogen plasma treated
a-Si:H(i) layers were deposited as the passivating layer on
both side, yielding about $1\%abs$ increase of η.
Additionally, the devices with various transparent
conductive oxide (TCO) upon nc-SiOx:H(n) single layer were
prepared and their IV parameters were compared. It was found
that lower contact resistivity of nc-SiOx:H(n)/TCO and
nc-SiOx:H/Ag are reached for the cells with titanium doped
indium oxide (ITiO) compared to the devices with ITO.
Besides, we identified the optimal thickness of the
magnesium fluoride (MgF2) and ITO for the cells with 10 nm
nc-SiOx:H(n) single layer by OPAL 2 simulation to maximize
the generate current. More than 0.6 mA/cm2 gain of Jsc and
$0.3\%abs$ increase of η were observed without compromising
to FF and Voc, achieving 40.06 mA/cm2 of Jsc and $22.8\%$ of
η. Furthermore, the perimeter recombination in the devices
with four 1.9×1.9 cm2 cells embedded in a quarter-M2-sized
wafer was stud- ied by means of Quokka3 simulation. About 9
mV reduction of Voc was found for the small size cells
compared with the full-size cells. Then we applied the
optimized ETL, ITO, a-Si:H(i) and a-Si:H(p) in the
full-sized M2 wafers to totally omit the perimeter
recombination. To further improve the device performance,
ultra-thin (5nm) nc-Si:H(n) film was utilized and optimized
in the full-sized SHJ solar cells. A TCO sputter damage was
observed for the cells with porous nc-Si:H(n) and proved to
be related to the ion bombardment and the microstructure of
nc-Si:H(n). By using a denser nc-Si:H(n), a decreased
sputter damage and an enhancement of η from $22.4\%$ to
$23.6\%$ were demonstrated. The best solar cell exhibits Voc
of 741.8 mV, FF of $82.2\%,$ Jsc of 39.27 mA/cm2 and η of
$23.95\%$ on an M2-sized wafer (244.3 cm2).},
cin = {615610},
ddc = {621.3},
cid = {$I:(DE-82)615610_20140620$},
pnm = {Verbundvorhaben: Street - Einsatz von hocheffizienten
Solarzellen in elektrisch betriebenen Nutzfahrzeugen;
Teilvorhaben: Herstellung und Entwicklung von (0324275E) /
Touch - Technologie- und Charakterisierungsplattform für
die Entwicklung von hoch-effizienten
Silizium-Heterostruktursolarzellen (0324351)},
pid = {G:(BMWi)0324275E / G:(BMWi)0324351},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
urn = {urn:nbn:de:hbz:5:2-1290542},
doi = {10.18154/RWTH-2023-10814},
url = {https://publications.rwth-aachen.de/record/973466},
}
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