Standing tall: This silicon microwire solar cell array grown with a copper catalyst is roughly twice as efficient as prior nanowire cells grown with a gold catalyst.
Caltech
New solar cells show gains in efficiency.
The race for inexpensive, highly efficient solar cells may have gained another contender in the form of silicon microwires. Efforts to develop ultra-thin wires that convert sunlight into electricity are not new to the solar power field, but a new method for growing the wires has roughly doubled their conversion efficiency and may hold the key for even larger gains.
"All wires thus far have had 1 or 2 percent efficiency [at the array level] with fundamental questions about whether they could ever go higher," says Nathan Lewis, a chemist at Caltech who coauthored the study, which appears in Science."We've demonstrated 3 percent efficiency and shown that there is no fundamental reason they can't perform at over 10 percent."
Silicon nanowires, or in this case slightly larger-diameter microwires, are typically grown from a silicon substrate with the help of tiny gold droplets. Under high temperatures, a single wire will quickly sprout from each droplet like a blade of grass. Gold is an excellent catalyst for wire growth, but it also introduces impurities that are generally believed to inhibit electron transport within the wires, reducing their overall efficiency.
Using copper instead of gold as the catalyst, Lewis and colleagues achieved roughly twice the efficiency of prior efforts in an array of wires. They believe the results are due to higher silicon purity and increased electron transport capacity compared to prior efforts that relied on gold catalysts.
In what they are calling a proof of concept study, the researchers kept the "packing fraction" of their array at 4 percent. Packing is a measure of how much of the surface of an array has wires protruding from it. A packing fraction of 4 percent means that 96 percent of the surface of the array has no wires and therefore is incapable of capturing sunlight and converting it into electricity. Lewis says that simply increasing the packing fraction to 15 to 20 percent will result in a fourfold increase in efficiency.
Some doubt it will be that simple. "If it's that easy, why haven't they done it?" asks Ray LaPierre a professor in the engineering physics department at McMaster University in Ontario. LaPierre says increasing the packing fraction is technically feasible through a technique known as "photolithography," but this would likely be prohibitively expensive for commercial solar cell production.
A new fabrication technique lets batteries use tin electrodes, and store more energy.
The flexible composite requires far less silicon than today's solar cells.
The new cells promise to be cheaper, more efficient, and even printable.
Guest (aarontco)
"simply increasing the packing fraction to 15 to 20 percent will result in a fourfold increase in efficiency"
Ahem, going from 4% to 20% is a *five-fold" increase people.
Sorry to quibble, aarontco, but actually the increase is the net of the max less the min, i.e. 20 - 4 = 16, which being 4x the min yields a four-fold increase.
I rankle whenever I see this common mistake repeated, especially by such seemingly educated persons in the media, in government, etc.
By the way, are you by chance an analyst for one of the banks which having been bailed out once are asking for more lest they fail (again)?
In the words of the great American philosopher, Jeff Foxworthy, "Are you smarter than a 5th grader?"
Best regards,
Maurice
What you just wrote makes no sense.
if a thing is 4 and you increase to 20, that is 5 fold.
By definition - doubling is 2 fold, triple is 3 fold, quadruple is 4 fold, quintuple is 5 fold.
Where did you get your definition?
Few things.
15-20 implies that details are NOT that precise.
You are probably right about usage of "fold" it uses variation of word "increase". It is like going from 100 to 200 is 100% increase but "increased to double" type of thing.
3rd is very likely that efficiency go down with increase in density at some point.
The efficiency in question is incoming-light/out-going-electrons.
The packing fraction is the density of wires on the surface.
Apples & Oranges
May I ask, is not the conversion efficiency a ratio of out-going energy / incoming energy, i.e.
out-going electrons / incoming light. I think CanT0ad may have stated the inverse of this.
CanT0ad's ratio > 1 because incoming > outgoing. This ratio is always < 1, or else we have discovered the perpetual motion machine.
He is correct that the conversion efficiency ought not be confused with the wire density.
They are indeed apples and oranges, but not totally unrelated. The electrons are the product which are processed and flow through the wire-pipeline.
It would seem correct to anticipate a cause and effect relationship, i.e. to expect that greater wire densities capturing greater quantities of light energy would produce greater quantities of electrons.
Whether this is a one to one relationship or not is of great import. We should follow this with great interest and keep it out of the hands of GE and other conglomerates who could bury it in archives, like the electric car they designed for NYC over a decade ago.
It would also be interesting to compare the concept to the Frankel Prism array which converts light into electrons. The emf is converted into laser energy, which beams have been transmitted across 60 mile distances near sea level, caught by antenna. These beams can be re-converted into emf for transmission and distribution through a grid.
Where are T Boone Pickens, "Oliver Warbucks" if I ever saw him, and his tribe to fund this research and development?
Keep it out of the hands of GE and the like or it will be buried.
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
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99 Comments
More silicon solutions
Ultimately, it is the silicon solutions that will win the competition to bring vast PV resources online. Thin-film and multi-junction options rely too heavily on rare elements.
Good research into new silicon technologies only helps. I wonder why we haven't heard as much about sliver technology and other means to dramatically reduce the silicon needed to produce similar amounts of electricity.
(By the way, telluride is not a metal, but tellurium is.)
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