Nanotechnology helps build solar cells

• If the nation decided to blanket its rooftops in solar cells --- generating as much as 75 percent of all electricity produced today --- it would be costly beyond belief and probably impossible: There isn't enough silicon.
• Scientists for 20 years have searched for an answer in very thin, plastic films, something that could be rolled out nationwide for a few cents per square foot.
• But they haven't proved very efficient at harvesting the power of the sun and tend to break down in air and sunlight.
• But lately, drawing on discoveries in the ultra-small world of nanotechnology, researchers have cooked up films full of tiny, energy-converting crystals that are durable and cheap to make.
• In today's edition of the prestigious journal Science, scientists at Lawrence Berkeley National Laboratory and the University of California, Berkeley, report making their solar cells out of crystalline nanotubes 100 times smaller than bacteria and capable of being tuned to a broad spectrum of light.
• The crystals are blended in a solution and dropped onto a spinning surface that spreads them into a film.
• But unlike plastics, the film is entirely inorganic so it doesn't degrade outdoors.
• And scientists for years have been building solar cells out of such nanotech materials as quantum dots, nanotubes and buckyballs, according to Ryne Rafaelle, director of the NanoPower Research Labs at the Rochester Institute of Technology.
• The efficiency at which the film turns sunlight to electricity is better than plastic-film solar cells but still very low at about 3 percent.
• But Berkeley scientists think they can raise that efficiency in time, according to Paul Alivisatos, a nanotechnology pioneer who was part of the team working on the film.