All the windows in every building in the world should be generating electricity for use on-the-spot to minimize electric bills, according to Massachusetts Institute of Technology. To do that, researchers there have demonstrated transparent solar cells that harvest the heat of the sun while allowing the visible light to pass through.
Much of the heat entering buildings in summer comes from the infrared wavelengths that are invisible, prompting MIT researchers to invent a transparent solar cell that absorbs only infrared. The organic material can be coated onto glass windows to harvest the infrared that would ordinarily heat up buildings, thus allowing the windows to function normally for visible wavelengths while simultaneously generating electricity from the infrared.
Smart windows will also sidestep the lion's share of the cost of manufacturing and installing solar cells. In fact, according to MIT, up to two-thirds of the cost of a typical solar cell installation goes for the glass and structural parts that make up the panels, a cost that is completely eliminated by smart windows which merely add a thin film on the inside layers of double-pane glass.
Smart windows have an invisible solar cell film that allows visible light to pass through unhindered, but converts the infrared (heat) rays into electricity.
Today, these organic films must be encased in glass to adequately protect them from contamination by oxygen and moisture in the air, but in the future impenetrable barrier films will safely encapsulate the material enabling retrofit kits that attach the transparent solar panels to the outside of windows. Labs worldwide are pursuing these barrier films for the manufacture of organic light-emitting-diode (OLED) displays, which today must be encased in glass to protect them. But barrier films will also allow thin-film solar cells to be fabricated on roll-to-roll manufacturing lines at a fraction of the cost incurred for traditional solar cells today.
The MIT researchers' prototype is claimed to one-up previous attempts with a new formulation for their solar cells that combines with infrared reflective coatings to achieve efficiencies that rival opaque organic photovoltaic cells. MIT is currently working to optimize its organic thin film formulation to realize its full potential, but its current prototype is still too inefficient for commercialization--at 1.7 percent. However, the team claims that theory predicts optimizations will boost efficiencies to 12 percent, making its optimized formula comparable to traditional solar cell installations, but at a fraction of the cost. And when barrier films become widely available, the optimized formulation of these transparent solar cells could be applied to both new and existing windows.
Funding was provided by the Center for Excitonics, an Energy Frontier Research Center funded by the U.S. Department of Energy.

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