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@PHDTHESIS{Li:803863,
author = {Li, Huimin},
othercontributors = {Rau, Uwe and Knoch, Joachim},
title = {{Z}inc oxide / nanocrystalline silicon contacts for silicon
heterojunction solar cells},
volume = {516},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH, Zentralbibliothek, Verlag},
reportid = {RWTH-2020-09928},
series = {Schriften des Forschungszentrums Jülich. Reihe Energie
$\&$ Umwelt},
pages = {1 Online-Ressource (VIII, 135 Seiten) : Illustrationen,
Diagramme},
year = {2020},
note = {Druckausgabe: 2020. - Onlineausgabe: 2020. - Auch
veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 2019},
abstract = {The silicon heterojunction (SHJ) solar cell is one of the
most promising technologies and drawsintensive attention due
to its high conversion efficiency with low temperature
coefficient and lowenergy consumption in production.
Reducing the cost of cell fabrication is one of the
keychallenges to overcome for mass production. Usage of
abundant materials and low-cost scalableproduction processes
is a way to reduce cost. This work is focused on the
replacement ofconventional indium tin oxide (ITO) with
aluminum-doped zinc oxide (AZO), which is a
moreenvironmentally friendly, abundant, and less costly
transparent conductive oxide material. Layersof AZO were
prepared with industrially relevant magnetron sputtering
process at low temperatureto address both scalability and
cost reduction for future production lines. Optical and
electronicproperties of AZO implemented in rear-emitter SHJ
solar cells is addressed in this study. To reduce parasitic
absorption of the window layer and form proper contact
between dopedsilicon (Si) layer and AZO, doped hydrogenated
nanocrystalline Si (n-type or p-type nc-Si:H)layers were
used in the SHJ solar cells instead of the conventional
doped hydrogenated amorphousSi (n-type or p-type a-Si:H)
layers. The optical and electrical properties of doped
nc-Si:H layersand AZO films were optimized for the
application in SHJ solar cells. Moreover, the influence
ofAZO sputtering on the passivation quality of Si layer
stacks was investigated and the contacts atthe interfaces
between AZO and p-type Si layers were studied. Furthermore,
loss analysis ofphotovoltaic parameters, such as open
circuit voltage (Voc), fill factor (FF), series resistance
(Rs),and short circuit current density (Jsc) of SHJ solar
cells with AZO was carried out after theexperimental
analysis.Various contact combinations between AZO and doped
Si layers were tested in SHJ solar cells.It was observed
that the solar cells with the combination of AZO and doped
amorphous Si layersor n-type nc-Si:H layer operated
properly. However, severe s-shaped illuminated current
densityvoltage(J-V) curves were observed in SHJ solar cells
when AZO was in contact with p-type nc-Si:H layers. The
s-shaped J-V characteristic is a result of a carrier
collection barrier at the rear sideof the device located at
the interface between p-type nc-Si:H and AZO. Increasing the
doping inp-type nc-Si:H layer or inserting a seed layer
prior to the p-type nc-Si:H layer resulted insuppression of
the contact barrier. However, increase of either the doping
concentration or thesputtering temperature of AZO films did
not contribute to the reduction of contact barrier. It was
observed that the AZO sputtering process during cell
fabrication affected the passivationquality of the cell
stack. Thus, effects of AZO sputtering temperature and
pressure on effectivecarrier lifetime were studied for
various combinations of AZO and doped Si layers.
Generally,high initial effective carrier lifetimes were
observed after Si layer deposition, but the lifetimeswere
significantly reduced upon AZO sputtering. However, the
detrimental effect of AZOsputtering on the lifetime of Si
layer stacks were eliminated completely by annealing
especially for room temperature AZO sputtering process. It
shows the application potential of roomtemperature sputtered
AZO in SHJ solar cells. Increasing the AZO sputtering
temperaturecontributed to the reduction or removal of
effective carrier lifetime degradation due to
in-situannealing. Variation of AZO sputtering pressure had
no influence on the lifetime variation.Compared to nc-Si:H
layers, amorphous Si layers were less sensitive to the
influence of AZOsputtering. With the application of AZO and
Si layers of n-type nc-Si:H and p-type a-Si:H, a cell
efficiencyof 21.2 $\%$ for a 19 mm × 19 mm cell was
achieved with Voc = 720 mV, Jsc = 39.1 mA/cm2 and FF= 75.4
$\%.$ A cell efficiency of 19.3 $\%$ for a large-area 156.75
mm × 156.75 mm cell was achievedwith Voc = 732 mV, Jsc =
36.2 mA/cm2 and FF = 72.8 $\%.$ The best cell results were
analyzed forlosses with respect to the state-of-the-art
theoretical limits. The loss in Voc is mainly due to
therecombination at the surface and in the bulk
(Shockley-Read-Hall), and due to the the non-optimalcarrier
selectivity at the contact interfaces with silicon layer
stacks. The loss in FF is mainly dueto the series resistance
and the recombination in the non-optimal junction region.
The seriesresistance is mainly due to the finger resistance
and the contact resistance at the interface betweenp-type Si
layer and AZO film. The loss in Jsc is primarily due to the
parasitic absorption in theshort and long wavelength
regions, the escape of long-wavelength light from the front
side of solarcell, and the front metal shadowing. The
present work demonstrates the feasibility to replace
conventional ITO with aluminum dopedzinc oxide (AZO), which
is prepared at room temperature with standard industrial
magnetronsputtering technique, in the process chain of
silicon heterojunction solar cells.},
cin = {615610},
ddc = {621.3},
cid = {$I:(DE-82)615610_20140620$},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
doi = {10.18154/RWTH-2020-09928},
url = {https://publications.rwth-aachen.de/record/803863},
}
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