Atmospheric plasma surface modification for continuous processing of solar cells
Atmospheric plasma surface
modification for continuous
processing of solar cells
by Rory A. Wolf, Enercon Industries Corporation, Menomonee Falls, Wisconsin, USA
introduction
polyethylenedioxythiophene (PEDOT)
The use of plasma surface
The use of plasmas in the fabrication of
and aluminum. Nanocrystalline cells use
modification technology in
photovoltaic cells is highly dependent upon
thin film materials and are overlaid on a
photovoltaic cell manufacturing
the materials employed and the processing
supporting matrix of conductive polymer
cycle requirement. For example, vacuum
has heretofore been used
or mesoporous metal oxide.
plasmas are not suitable for use in solar
primarily in applications
• Composite (Hybrid) Photovoltaic
cell processing when high throughput on
Technology—One example is the use of
such as the deposition of
a continuous basis is required. Vacuum
polymers with nano-particles to make a
amorphous hydrogenated
plasma chambers built for SiNx deposition
single multi-spectrum layer which can
silicon nitride (SiN) layers in are typically batch-process related, but are
be stacked to make multi-spectrum solar
a vacuum plasma-enhanced also designed to work in a semi-continuous
cells.
chemical vapor deposition
mode through the intermittent exchange
(PECVD) process to create
of treatment materials within the vacuum
Bulk silicon technologies, such as those
anti-reflection and surface
chamber after the treatment is completed
employing wafer-based manufacturing,
(and bulk) passivation on
and once atmospheric pressure is returned.
feature self-supporting wafers between 180
thin-film solar cells, or the
However, this process is still not economical
to 240 micrometers thick that are processed
for high throughput plasma surface etching,
and then soldered together to form a solar
use of vacuum plasma etch-
cleaning and functionalization.
cell module. Organic and polymer solar cells
ing in barrel-type reactors to
There are at least four major generations
are built from thin films (typically 100 nm)
perform edge isolation in some
of photovoltaic cells whose materials define
of organic semiconductors, such as poly-
remaining fabrication processes.
the application of plasma technology to
mers, and small-molecule compounds like
As photovoltaic cell manufac- their fabrication. They are:
polyphenylene vinylene, copper phthalocya-
turing processes evolve, and
nine (a blue or green organic pigment) and
• Large-Area, Single Layer P-N Junction
with the added pressures of
carbon fullerness. Considering the wide
Diode—Typically made using a silicon
increasing hazardous chemical
range of materials employed to maximize
wafer and the dominant technology in
solar efficiencies, the ability to integrate the
waste disposal costs, there has
the commercial production of solar cells,
completely continuous in-line manufactur-
been interest in atmospheric
accounting for more than 86% of the
ing of rigid panel and flexible solar cells
plasma systems as efficient solar cell market.
by utilizing a variable chemistry surface
dry etching, surface cleaning
• Rigid and Flexible Thin-Film Solar
modification technique relative to complex
and adhesion promotion pro-
Cells—Semiconductor deposition materi-
material constructions holds the prospect of
cess tools. This paper exam-
als used include amorphous silicon,
significantly reducing manufacturing costs.
ines these systems and details
polycrystalline silicon, micro-crystalline
Atmospheric pressure gas phase plasma tech-
etching, cleaning and bonding
silicon, cadmium telluride, and copper
nology will therefore become essential for
trial data confirming system
indium selenide/sulfide. Typically, the
future in-line manufacturing of solar cells if
top surface is low iron solar glass for rigid
efficacies.
major reductions in fabrication costs are to
cells (a fluoropolymer for flexible cells),
be achieved.
the encapsulant is crosslinkable Ethylene-
vinyl acetate (EVA), and the rear layer is
Plasma treatment
a Tedlar- PET-Tedlar laminate (although
Atmospheric plasma treatment (APT) devic-
Keywords: Solar Cell
glass, coated PET or another bondable
es allow for completely homogenous surface
Processing, Photovoltaic Cell
polymeric film are also used).
modification without filamentary discharges
Manufacturing, Plasma
• Photoelectrochemical, Polymer and
(known as streamers), because a uniform
Surface Modification Nanocrystal Cells—Do not rely on a
and homogenous high-density plasma at
traditional p-n junction to separate
atmospheric pressure and low temperature is
photo-generated charge carriers. Polymer
produced. In Figure 1, a comparison between
cell materials used include polyester
corona discharge and plasma is shown.
(PET) foil, indium tin oxide (ITO) film,
The APT process modifies material sur-
8 – Global Solar Technology – September/October 2008 www.globalsolartechnology.com
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