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Nonactive solar materials make a difference

Photonics Spectra
Dec 2009
Anne L. Fischer, Senior Editor, anne.fischer@laurin.com

In the never-ending quest to lower costs and boost efficiency in solar modules, attention is focused on the active-layer materials such as silicon wafers or copper indium gallium selenide thin films. Nonactive materials, however, can account for nearly half of the module materials cost, and, thus, interest is turning to the development of lower cost/higher efficiency materials such as encapsulants, metallization, antireflection coatings and transparent conducting oxides.

In the report Driving Down Solar Costs: Non-active Material Opportunities by Lux Research Inc. of Boston, analysts looked at 21 new nonactive materials for the solar market in terms of their potential effect on the dollar-per-watt cost, factoring in how long it will be before the material is ready for commercialization. When asked how nonactive materials can have much of an effect on cost or efficiency, Johanna Schmidtke, the report’s author, said that the goal is to increase efficiency for a relatively small amount of money.

Greenlight2.jpg
New materials, such as the metallization paste shown here adding grid lines to the front of silicon solar cells, boost their efficiency. Photo courtesy of DuPont.

As an example, she cited antireflection coatings for external reflectivity of glass on the module, which she said are quite expensive. But she added, “Once you get to a certain point in module efficiency, the cost per area is low enough to make sense in terms of dollars per watt.”

New twist on old tech

Key findings in the report include the fact that tomorrow’s nonactive products will be improvements upon today’s technologies, and anything that’s really new will have to show significant cost savings and efficiency improvement before finding widespread adoption. For example, in metallization, there are new ways of adding grid lines to the front of crystalline silicon solar cells, such as screen printing very fine lines.

Schmidtke pointed out that making the grid lines thinner allows for less shading on the cell and, therefore, greater efficiency. Screen printing is a proven technology in creating fine lines, and adopting processes that are advanced variations on screen printing doesn’t require a leap of faith on the part of module manufacturers, but moving to any noncontact printing method will take at least three to five years before it meets market acceptance.

Two new processes looking to replace screen printing are inkjet printing and aerosol jet printing, but they will have to prove their value before finding wide use in the solar industry. Xjet, a company based in Israel, has an inkjet metallization process for solar cell manufacturing. One company that makes an aerosol jet system for solar manufacturing is Optomec of Albuquerque, N.M. The system is currently installed in an R&D production line at the Fraunhofer Institute for Ceramic Technologies and Systems in Dresden, Germany, the results of which may help get other manufacturers onboard with the new technology.

Typical time to market for any totally new material or process is five years or more, according to Schmidtke. From the solar vendor’s point of view, when the module has to “sit out there for 20 years in rain, dust and wind, it has to have a durability and performance that’s suitable for its warranty.” It’s no wonder that the materials in use today are variants of the tried and true. But with some of the newer, more radical materials showing great promise, the makeup of solar modules could look very different five years from now, and a lower cost and more efficient source of energy could be the result.


GLOSSARY
glass
A noncrystalline, inorganic mixture of various metallic oxides fused by heating with glassifiers such as silica, or boric or phosphoric oxides. Common window or bottle glass is a mixture of soda, lime and sand, melted and cast, rolled or blown to shape. Most glasses are transparent in the visible spectrum and up to about 2.5 µm in the infrared, but some are opaque such as natural obsidian; these are, nevertheless, useful as mirror blanks. Traces of some elements such as cobalt, copper and...
thin film
A thin layer of a substance deposited on an insulating base in a vacuum by a microelectronic process. Thin films are most commonly used for antireflection, achromatic beamsplitters, color filters, narrow passband filters, semitransparent mirrors, heat control filters, high reflectivity mirrors, polarizers and reflection filters.
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