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U.S. Laser Corporation - Continual Support for the Solar Photovoltaic Industry

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• Solar Cell Processing Video Presentations
• Thin Film Solar Panel Laser Scribing System Production Machine Design Concept

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 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 Corp's involvement with the solar photovoltaic industry include:

• Delivery of equipment and/or process development to the following major industry groups:

• Delivery of Single and Multiple Beam Laser Systems, for panels up to 3 1/2' x 5' (1.0 x 1.5 m), with scribing speeds in excess of 30"/s.
• Delivery of Single and Dual-Wavelength Systems for selective scribing applications. Invention of "Quick Change" frequency doubling optics to facilitate selective scribing.
• Delivery of Turnkey Systems with panel load and unload.
• Delivery of Multiple Beam systems for greatly reduced processing times.

Through our applications development laboratory and customer support, we keep abreast of current and evolving technologies in the fields of both crystalline silicon (c-Si), and thin film technologies, such as amorphous silicon (a-Si), cadmium telluride (CdTe), copper indium gallium selenide (CIGS) and other emerging technologies.

SYSTEMS FOR PROCESSING CRYSTALLINE SILICON SOLAR CELLS

Systems for processing c-Si solar cells generally have a smaller system footprint than thin film processing systems due to the smaller X-Y table size requirement for the typical 150mm X 150mm cell. While most common systems are built around lasers operating at a single wavelength, dual wavelength systems are also available for customers performing R&D or requiring maximum flexibiltity. Typical applications include edge isolation, laser grooved buried contacts (LGBC), and wafer cutting.

Laser Systems for Large Thin Film Photovoltaic Panels

U.S. Laser Corp. has designed and manufactured many different system configurations for processing large glass panels. Panel sizes up to 150cm x 100cm (60"x40") can be accommodated with standard designs. Larger panels can be handled with minimal new design effort. Although most high volume, solar cell panels are large flat glass substrates, some of the examples below indicate some of our possibilities and capabilities.

Typical Large Glass Panel Scribing

The work horse in this class of equipment is a split axis X-Y motion system with one or more laser beams. The glass panel is loaded (either manually or using precise automated glass handlers) onto a holding chuck or platform. The chuck is the surface of a high speed linear stage that moves the panel under the laser beam or beams. The laser beam focusing hardware is mounted to a cross axis bridge and steps across the panel to the next scribe line location at the end of each linear transition of the panel. Using multiple beams and high speed linear motor stages, a 150cm long panel may be fully scribed in 30 seconds.

U.S. Laser offers various panel holding chucks for these applications. Chucks may be provided for top-side scribing or through the glass scribing. In all cases debris collection suction systems and laser lens purging nozzles are integrated into the machines.

Depending upon the customer's needs, their system can be provided with the laser beams beneath the panels, such that the beams point up. This configuration generally is incorporated for through the glass processing.

Rapid Scribing For Curved Panels

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

Multiple Beam Delivery for Simultaneous Scribes

This optical system is designed to take the output of 1, 2, or 4 lasers to produce up to 8 balanced beams, allowing for simultaneous scribing of 8 lines. Each beam can include a constant power feedback control, and coaxial parfocal CCTV viewing. The design is to be used with a split axis moving table/moving beam.

• Number of Beams: up to 8
• Number of Lasers: 1, 2, or 4
• Nominal Beam Spacing: 10 cm (adjustable), alternate spacing available

Economical System for Moderate Throughput

Where high scribing speeds are not required, these systems are 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.

• Number of Beams: 1-2
• Motion Control System: XY, including two axis interpolated moves. Plus Manual z (focus) axis.
• Maximum Scribing Speed: 10 "/s (25 cm/s) standard. (>20 "/sec. with linear motors)

Research and Development Machines:

U.S. Laser also offers a series of R&D, and small production run machines for small glass panels, amorphous silicon cells, and silicon wafer processing. These machines generally are single beam systems with X-Y table panel positioning. Scribing speeds above 30 in/sec are available, and motion axes to 24” x 24” will fit in a standard frame. A long list of Nd:VO4 or Nd:YAG lasers are offered; and U.S. Laser’s technical staff can choose or recommend a laser in accord with the application.

Numerous beam shaping, attenuating, and focusing options are available; as well as variable focused spot sizes, and dual wavelength (1.06µ and .532µ) features are offered.

Lasers for Processing Photovoltaic Panels

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.

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 or Nd:Vanadate 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 or vanadate laser, which emits in the green spectrum. 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 diode pumped Nd:YAG and Nd:YV0₄ lasers, appropriate for the laser scribing processes. All are AO Q-switched, CW pumped TEM₀₀ lasers. Both fundamental wavelength (near infrared, 1.064 um) and frequency multiplied (green, 0.532 um) and UV (0.355 µm and 0.266 µm) versions are available, in a variety of output powers and pulsewidths.

Contact U.S. Laser Corp. Sales Dept. for available Nd:YVO4 lasers.

Available Diode pumped Nd:YAG lasers for low speed systems are summarized in the table below.

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