Back in February, Lexington, MA-based solar energy startup 1366 Technologies won an award from the U.S. Department of Energy worth as much as $3 million. The catch: it had to show that its techniques for making more efficient photovoltaic cells, born in the laboratory of MIT mechanical engineer Emanuel “Ely” Sachs, would actually work on an industrial scale.
Today the venture-backed company revealed that it has hit one of the biggest milestones toward collecting the full DOE award—producing high-efficiency photovoltaic cells in 6-by-6-inch wafers, the standard size used in solar panels—ahead of schedule. The company also took the wraps off the two methods it’s using to make the cells more efficient, information that had been closely guarded until now.
Unlike many of the other solar technology companies in the Boston area, 1366 isn’t trying to reinvent the material used in photovoltaic panels: plain silicon that comes in either an expensive “monocrystalline” variety (a single big crystal) or a cheaper “multicrystalline” form (the type chosen by 1366). The two techniques pioneered by the company, according to Craig Lund, the startup’s director of business development, are purely mechanical, involving texturing the surface of cells to trap more light and reducing the width of the metal wires that manufacturers lay across the cells’ surfaces to collect free electrons.
The company’s first technology—texturing—etches silicon wafers with a honeycomb pattern that refracts more light into the base of the cell. The pattern is geometrically optimized to capture light without creating too many pits, walls, or discontinuities where electrons would wind up pooling and dissipating, Lund says.
1366’s second innovation is a new way of laying down the fingers or “metallization lines” that stretch across the surfaces of solar cells, creating a path to siphon off electrons. Fingers created using traditional screen-printing processes are about 120 microns wide, which means they end up shading about 9 percent of a cell’s surface, so only 91 percent of the surface is available to generate electricity. Sachs developed an electroplating process in which a seed layer of bulk metal (usually silver or copper) is glued to the silicon, then the rest of the wire is built up in layers. The resulting fingers are only 30 microns across, meaning they shade only 2 percent of the surface.
The honeycomb texturing technique by itself, increases overall solar cell efficiency by 1 percent, while making the metallization lines thinner boosts efficiency by another 1 percent or more, according to an announcement released today by 1366.
The company’s ultimate business will be to make and sell texturing and metallization machines that solar cell manufacturers can incorporate into their existing assembly lines. “The big news for us is that we’re going into commercial production with equipment that [when used together] delivers an 18-percent multicrystalline cell,” Lund says. In other words,
