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

• 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 2' x 5' (0.6 x 1.5 m), with scribing speeds in excess of 14"/s (35 cm/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.

Through our applications laboratory and customer support, we keep abreast of the evolving photovoltaic technologies, including thin-film amorphous silicon, cadmium telluride, and other thin film materials.

Laser Systems for Large Photovoltaic Panels

U.S. Laser Corp. has designed and manufactured many different system configurations for processing large (~60 cm x 150 cm) panels. These three examples indicate the range of possibilities and capabilities:

Rapid Scribing Speed For Flat and 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 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)

Economical System for Moderate Throughput

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.

• Number of Beams: 1-2

• Motion Control System: XY, including two axis interpolated moves.

• Maximum Scribing Speed: 10 "/s (25 cm/s) standard. (16"/s to 20 "/s with linear motors)

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 (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 and Nd:YV0₄ lasers, both lamp and diode pumped, 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 um and 0.266 um) versions are available, in a variety of output powers and pulsewidths.

Diode pumped laser versions are summarized in the table below.

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