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U.S. Laser Corp. has been providing
equipment and expertise to the solar photovoltaic industry since 1980, when we
delivered our first laser scribing system to Solarex. During the ensuing 18
years, we have continued to develop new technologies to improve speed and
quality, and to support the evolution of new materials and processes.
Highlights of U.S. Laser's 18 year
involvement with the solar photovoltaic industry include:
- Delivery of equipment and/or process
development to the following major industry groups:
Ametek
BP
Solar (formerly Advanced Photovoltaic Systems)
Chronar
Lockheed
Martin
Polyplex
Corp. Ltd. (through Materials Research Group)
Siemens
Solar (formerly Arco Solar)
Solar
Cells, Inc.
Solarex
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Delivery of Single and
Multiple Beam Laser Systems, for panels up to 2' x 5' (0.6 x 1.5 m), with
scribing speeds in excess of 10"/s (0.25 m/s).
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Delivery of Single and
Dual-Wavelength Systems for selective scribing applications. Invention of
"Quick Change" frequency doubling optics to facilitate selective
scribing.
Through our
applications laboratory and customer support, we keep abreast of the evolving
photovoltaic technologies, including thin-film amorphous silicon and cadmium
telluride.
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This system features a high speed (40 cm/s) two axis
(YZ) moving beam system
with a single (X) axis moving table, all on a rigid granite structure. The laser
can be configured for fundamental wavelength or frequency doubled mode. The beam
delivery system features coaxial, parfocal CCTV viewing.
- Number of Beams: 1
- Motion Control System: XYZ, including three axis interpolated moves.
- Maximum Scribing Speed: 40 cm/s
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This optical system is designed to take the output of 2 or 4 lasers to
produce 8 balanced beams, allowing for simultaneous scribing of 8 lines. Each
beam includes a constant power feedback control, and coaxial parfocal CCTV
viewing. It is designed to be used with a 2-axis (XY) moving table.
- Number of Beams: 8
- Number of Lasers: 2 or 4
- Nominal Beam Spacing: 10 cm (adjustable)
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Where high scribing speeds are not required, this system is
very economical. The laser and 2 axis (XY) table are supported on a large welded
steel frame. The table can be fitted with a vacuum holddown for flexible panels.
The beam delivery system, including coaxial parfocal CCTV viewing, can deliver
one or two beams. The system can be outfitted with a mechanical scribe head.
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Modern photovoltaic panels are large multilayer devices
manufactured in high volume by various deposition methods. A light-sensitive
semiconductor material such as amorphous silicon or cadmium telluride is
sandwiched between two electrical conductors (one transparent, one highly
reflective) to form a light driven battery. For maximum efficiency, the panel is
electrically divided into many strips, connected in series. The isolation of the
individual strips and the series connections are created by selective laser
scribing steps.
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The first process scribes the front electrode, generally made
of tin oxide. Since this layer is transparent in the visible, a fundamental
wavelength Nd:YAG laser (output in the near infrared) is generally used.
The second process scribes the semiconductor material
(amorphous silicon, cadmium telluride, or other material). Since this material
absorbs in the visible portion of the spectrum, it can be scribed with a
frequency-doubled Nd:YAG laser, which emits in the green. Some manufacturers
scribe this layer in the near infrared, however.
The final layer to be scribed is the back electrode,
typically a deposited metal such as aluminum. Different manufacturers use widely
different scribing parameters (wavelength, power, pulse width) for this layer,
as the results depend strongly on the materials and geometry of the panel.
In considering the appropriate
laser(s) for processing
particular panels, the following parameters should be considered: materials and
thickness of the layers, scribe width, requirements, number of beams from each
laser, and scribe speed.
U.S. Laser Corp. offers a range of Nd:YAG lasers appropriate
for the laser scribing processes. All are AO Q-switched, CW pumped TEM00
Nd:YAG lasers. Both fundamental wavelength (near infrared, 1.064 Fm)
and frequency multiplied (green, 0.532 Fm
and UV, 0.355 µm and 0.266 µm) versions are available, in a variety of output
powers and pulsewidths. These are summarized in the table below.
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