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A Step Closer To The Optimum Solar Cell
An anonymous reader writes "Besides cost, solar cell efficiency is the second most critical criteria. Scientists from Berkeley Lab and other institutions, have announced a new solar cell material that may be able to achieve an extraordinary efficiency of about 50 percent -- twice the amount of the current record holder."
In 1999, Walukiewicz and others at Berkeley Lab were working with solar-cell designers at DOE's National Renewable Energy Laboratory, who were trying to build a three-junction cell. The NREL researchers inadvertently created the first photovoltaic semiconductor with a split band gap. But at first they didn't realize it.
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"They needed a new material with a 1-eV band gap and a crystal lattice structure that matched the other layers of the cell," Walukiewicz explains. "They used gallium indium arsenide nitride alloys in which just a little nitrogen could achieve the desired band gap, and an almost perfect lattice match."
Since the band-gap reduction was unexpected, Walukiewicz set out to find out how it worked. The answer, it developed, was that the few atoms of nitrogen, which are much more electronegative than the host atoms (much more strongly attractive to electrons) produced a narrow energy band of their own, splitting the GaInAs conduction band into two parts. The gap to the lower of the two conduction bands was the desired 1 eV.
In the case of GaInAs, other characteristics of the split bands made for a poor solar cell material. Nevertheless, Walukiewicz and his colleagues continued to investigate the phenomenon and developed a model of the split-band phenomenon known as "band anticrossing."
Yu admits that forming highly mismatched alloys is "challenging from a crystal-growth point of view," but there is hope that crystals can be grown epitaxially (the growth on a crystalline substrate of a crystalline substance that mimics the orientation of the substrate). One good sign, he says, is that Japanese researchers have already grown thick oxygen-doped crystals of a related material, zinc selenium.
http://tinyurl.com/4ny52
The ROI (for retail and manufacture cost) and the Enviromental impact of production is addressed.
Granted the source is an RE magazine, but they do list references on some of the studies if you want to follow up.
The panels you can buy and use for your house today have a 3-4 year energy payoff. (ie, they make an amount of energy equal to what was put in to them in production) They last in the neighborhood of 20-30 years.
There are some nasty chemicals required for production. The total environmental impact, however, is significantly smaller than obtaining the same lifetime amount of power from any other source available. The waste produced by a similar amount of power from coal, nuclear, gas, etc... over a similar lifetime is significantly larger.
The pollution only happens once, for 20-30 years worth of power. The pollution from any other option doesn't stop unless you stop using it.
Anyway, this is a discussion on solar cells, which lend themselves to distributed power generation of some form or another - they don't have to be big. More efficiency there makes the solar powered laptop easier to acheive.
- Cu, In, Ga, Se and S are deposited via a vacuum & diffusion process
- Can be deposited on plain glass (same stuff used for window panes)
- 1 micron of this stuff absorbs more sunlight than 350 microns of Si (about 99% of light - don't know how this translates to efficiency, though - article not too technical).
- Panels like these would cost roughly a tenth of the price of those currently available.
- Pilot plant for manufacturing was expected to begin manufacturing somewhere in April (this month), manufacturing panels 400mm x 500mm @ 20W
- Pilot plant (100 sq m) to cost about US$ 2.3 - probably within reach for many developing countries.
Unfortunalty there's not much more detail or Web references....Free, as in your money being freed from the confines of your account.