By Bud Coburn
OSCs utilize windows as collectors, directing light energy to solar cells in the window frames. To accomplish this, a special dye is affixed to the surface of a piece of the glass, which is then exposed to a light source. The dye absorbs incoming light and re-emits it inside the glass, where it bounces along until it reaches the edge. There, awaiting the absorbed light, is a thin layer of solar cells, which converts the light into electricity. The bouncing of the light is described by a principle known as “internal refraction,” which is the same phenomenon that keeps light trapped in optic fibers.
This design is essentially an evolved form of an idea that was abandoned in the 1970s, known as luminescent solar concentration. These early experiments failed because collected light was absorbed before it reached the edges of the glass (or plastic) plates. The MIT team solved this problem by adding a small concentration of dye that collects the absorbed light from its surrounding dye. They also introduced a new class of dye molecules, known as molecular phosphors, which are exceptionally transparent to their own light emission.
This innovation offers a contrasting approach to traditional solar concentrators, which use mirrors to concentrate sunlight onto solar panels. These devices are large and expensive, which limit their utility. Specifically, they rely on bulky sun-tracking mirrors that aren’t feasible in most residential settings. OSCs perform the same function as solar concentrators, but they lack the problems that make their predecessors cost-prohibitive and unwieldy.
For now, the team must deal withtechnical complications, some of which are described below:
- The dyes would degrade natural lighting by preventing 90% of sunlight from entering the room. Windows dyed in this way would appear as smoked glass, which some may find objectionable.
- If too much dye is used, some of the light may be re-absorbed before it reaches the solar cells.
- Currently, the devices are not stable for a long enough period to be ready for mass production. Researchers tested one model and found that it was only effective (up to 92% performance) for three months. The next design will incorporate technology developed for organic light-emitting devices to increase longevity.