Scientists at the Lawrence Berkeley National Laboratory in California took an unconventional approach in their bid to design the world's most efficient solar cell. Instead of developing a device that can absorb as much light (or photons) as possible they created a solar cell that emits more light, Talking Points Memo recently reported. Their solution: Fluorescence.
Sunlight absorbed in a solar cell produces electrons that must be extracted as electricity. If electrons aren't removed fast enough, they decay and release their energy. If that energy is released as heat -- which it typically is -- the solar cell produces less power.
Scientist found that fluorescent light -- which consists of photons, yet isn't visible under normal conditions -- was the key to unlocking the efficiency puzzle. Scientist Owen Miller figured out that if the released energy left the solar cell as external fluorescence, it would boost its voltage. Eli Yablonovitch, the Berkeley lab electrical engineer who led the research, put it this way in a recent feature published by LBNL, "The better a solar cell is at emitting photons, the higher its voltage and the greater efficiency it can produce."
Theoretically, the most efficient single junction solar cell -- which uses a single material to collect light -- could convert about 33.5 percent of the energy it absorbs into electricity. Miller discovered that using a rare material called gallium arsenide as a semiconductor helped hit that sweet spot between the amount of light absorbed and the amount converted to electricity and is capable of hitting that solar efficiency limit.
Alta Devices, a private company co-founded by Yablonovitch, has fabricated fluorescent solar cells from gallium arsenide that achieved a record conversion efficiency of 28.4 percent. That's 5 percent more efficiency than solar cells in commercial use today that are made from monocrystalline silicon wafers, according to LBNL.
Of course, there are challenges to manufacturing these fluorescent solar cells -- namely that gallium arsenide is far more expensive than the commonly used solar cell material silicon. This is the same conundrum faced by every other non-silicon solar panel maker. Companies like First Solar, which uses cadmium telluride, are able to offset the cost of the material because the solar panels are more efficient than ones made with silicon.
Yablonovitch, not surprisingly, makes the same argument for gallium arsenide, which he says absorbs photons "10,000 times more strongly than silicon for a given thickness, but is not 10,000 times more expensive."
[via Talking Points Memo; Lawrence Berkeley National Laboratory]
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