Application of Randomly Firing Jet Arrays for Electrodeposition
S. Delbos,
a,z
P.-P. Grand,
a
E. Chassaing,
a
V. Weitbrecht,
b,c
T. Bleninger,
b
G. H. Jirka,
b
D. Lincot,
a,
*
and O. Kerrec
a
a
Institute of Research and Development on Photovoltaic Energy, Unité Mixte de Recherche Électricité de
France/Centre National de la Recherche Scientifique/École Nationale Supérieure de Chimie de
Paris (UMR 7174 EDF-CNRS-ENSCP), EDF Research and Development, 78400 Chatou, France
b
Institut für Hydromechanik, Universität Karlsruhe, D-76128 Karlsruhe, Deutschland
c
VA für Wasserbau/Hydrologie/Glaziologie, 8092 Zürich, Switzerland
Randomly firing jet arrays can be used for large-scale electrodeposition from dilute solutions for which tertiary current distribution
prevails, for example, the electrodeposition of Cu–In–Se layers, which are promising compounds for thin-layer solar devices. For
this type of electrodeposition, a stirring system is needed to enhance the mass-transfer rate toward the cathode. The studied stirring
system is a modular jet array firing in the horizontal direction, submerged in the tank containing the electrolyte. A dilute Cu
electrolyte was used to investigate and optimize the hydrodynamic conditions determined by the stirring system. Two parameters
were investigated to vary the hydrodynamic conditions: the mesh of the jet nozzles and the distance between the jet nozzles and
the cathode. An optimized configuration was found, allowing the jets to merge and create a homogeneous tertiary distribution.
Random sequential activation of the jets was used with the optimized configuration, and the resulting copper layer exhibited higher
homogeneity than those resulting from continuous activation of the jets.
© 2009 The Electrochemical Society. DOI: 10.1149/1.3208057 All rights reserved.
Manuscript submitted June 5, 2009; revised manuscript received July 15, 2009. Published September 14, 2009.
Electrochemical processes are used for different purposes:
Chemical production, surface finishing treatment, and more recently,
functional thin-film deposition. In particular, copper damascene in-
terconnects and thin-film magnetic alloys are usually synthesized by
electrodeposition.
1
More recently, semiconductor thin films are also
prepared by electrodeposition.
2
In the photovoltaic field for industrial development, the elec-
trodeposition of semiconductor thin films should be performed on
large-scale surfaces, i.e., surfaces larger than 1 m
2
. For such up-
scaled processes, the current distribution is a key issue because ho-
mogeneity of electrodeposited layers is important for the yield of the
process. Among the parameters responsible for the current distribu-
tion, mass-transfer phenomena can be critical in dilute electrolytes
especially in the deposition of multinary compounds.
3,4
When at
least one of the electroactive species deposits under diffusion con-
trol, it is necessary to enhance the mass-transfer rate toward the
cathode by a stirring system. One of the challenges is to create
homogeneous hydrodynamic conditions to synthesize homogeneous
electrodeposited layers.
3
These requirements are well fulfilled for small surfaces and well-
controlled hydrodynamic conditions, as in rotating disk electrode
experiments,
5
but they are much more difficult to achieve for large-
scale electrodeposition processes 1m
2
. An appropriate investi-
gation of the hydrodynamic conditions is necessary to better control
the process.
6
Different stirring systems can be used to enhance the mass trans-
fer toward the deposition surface. One of the most used and patented
for industrial thin-film alloy electrodeposition is the paddle cell:
7,8
A
paddle reciprocates near the deposition surface. Other systems are
used as well, for example, the multijet system.
9
In one of the most
investigated stirring systems, the paddle-cell, experimental,
10,11
and
numerical
12
studies are aimed at optimizing experimental conditions
and create homogeneous hydrodynamic conditions in the paddle
cell. An adaptation of this system is the comblike system: Several
paddles are fitted together and allow for a decrease in the amplitude
of the stroke.
13
Another system suitable for scaling up diffusion-controlled thin-
film electrodeposition processes is the jet array system:
6
An array of
jets firing in the same direction, each with the same flow rate. One-
dimensional jet arrays are typically perforated pipes diffusers and
two-dimensional 2D jet arrays can be described as perforated
plates. We already investigated the flow conditions for this system in
different experimental conditions and optimized the system for best
turbulence intensity and lowest mean flow.
6
To test the suitability of random jet arrays for diffusion-
controlled thin-film electrodeposition, a dilute copper–nickel sulfate
electrolyte with citrate as a complexing agent was developed.
14
It is
routinely used in our laboratory to test stirring systems. A citrate
complexing agent is added to bring the deposition potentials for Cu
and Ni closer, but Cu nevertheless remains substantially nobler. As a
result, Cu is typically discharged under mass-transfer control,
whereas Ni deposition remains under charge-transfer control over a
significant potential range.
15-17
Copper and nickel form a continuous
solid solution and Cu–Ni deposits from citrate electrolytes are
single-phase alloys. In this study our goal was to investigate the
effect of the stirring system on mass-transfer and current distribu-
tion; hence the deposition potential was chosen so as to deposit
almost only copper.
Current Distributions
In our laboratory, thin-layer solar cells based on electrodeposited
Cu–In–Se can reach a conversion efficiency up to 11.4% on small
surface areas.
18
For an industrial development, a scaling up of these
results is needed and especially homogeneous composition and
thickness on large surfaces, up to 1 m
2
. Generally, scaling up in
electrodeposition leads to current distribution issues, especially in
the electronic industry, such as electrodeposition of copper intercon-
nections or electrodeposition of magnetic Fe–Ni alloys.
1,3
The inhomogeneities of thickness and composition in the elec-
trodeposition processes are linked to the current distribution.
19
Dif-
ferent parameters, such as electrolyzer geometry, electrode resistiv-
ity, charge-transfer resistance, and hydrodynamics, can play a role in
the current distribution.
19
A typical resistance is associated with each
parameter, and the comparison of these resistances allows the deter-
mination of the dominant feature of the electrodeposition system
Table I.
When the electrolyte resistance is the dominant feature of the
system, the current distribution is determined by the electrolyzer
geometry, usually leading to increased thickness on the edges of the
working electrode.
20
This case is called “primary distribution.”
When the charge-transfer resistance is of the same order of magni-
tude as the electrolyte resistance, the primary distribution is
smoothed and the edge effect is damped in the “secondary distri-
bution”. The Wagner number W
a
can be used to compare the acti-
vation resistance to the electrolyte resistance
* Electrochemical Society Active Member.
z
E-mail: sebastien.delbos@edf.fr.
Journal of The Electrochemical Society, 156 11 E161-E166 2009
0013-4651/2009/15611/E161/6/$25.00 © The Electrochemical Society
E161
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