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.”