Bars on a solar cell's surface collect current. The light-absorbing dyes inside the cell can be of various decorative colors. (Courtesy of Winfried Hoffmann)

The next building material to generate solar power may be windows. In a dye-sensitized solar cell, dye molecules attached to nanoscale titania particles are held between two panes of glass; the dye absorbs light and releases electrons, which are harvested by the ­titania. The basic concept was invented 15 years ago by Michaël ­Grätzel, chemistry professor at the École Polytechnique Fédérale de Lausanne in Switzerland. Now, the technology is in limited production by Konarka, a company based in ­Lowell, MA, and will soon be more widely available. "The normal configuration has glass on both sides and can be made to look like a colored glass," Grätzel says. "This could be used as a power-producing window or skylights or building facades. The wall or window itself is photovoltaically active." This could give a whole new meaning to the term "power windows."

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