Nanotechnology Boosts Solar Cell Performance

Roland Piquepaille writes "Physicists from the University of Illinois at Urbana-Champaign (UIUC) say they have improved the performance of solar cells by 60 percent. And they obtained this spectacular result by using a very simple trick. They've coated the solar cells with a film of 1-nanometer thick silicon fluorescing nanoparticles. The researchers also said that this process could be easily incorporated into the manufacturing process of solar cells with very little additional cost. Read more for additional references and a photo of a researcher holding a silicon solar cell coated with a film of silicon nanoparticles."

Oh no, it's Roland again!

[Baddas (243852)]

I wish I had access to the slashdot front page for my articles.

Re:Try reading the article.

[Baddas (243852)]

It only bothers me because he linkjacks it with his blog.

If he was just posting an article, with a link to the EurekAlert post, it'd be all good. Instead, he has to post about his spammy blog, as well as his (paid?) blog on ZDnet.

The ratio of decent links to spam is 1:2 in this article.

Re:Try reading the article.

[Baddas (243852)]

Also, he doesn't post the whole story (60% improvement in the UV spectrum) but rather the more sensational version (60% improvement!). That's pretty dishonest.

Re:

[Baddas (243852)]

Big difference between posting something original on a blog with ads, and paraphrasing an article on your own ad-filled blog solely for the revenue.

If I went around ripping off the AP, I'd get a nastygram from their lawyers. Why do we tolerate it more when it's a creepy-looking Frenchman?

Re:

[nuzak (959558)]

Big difference between posting something original on a blog with ads, and paraphrasing an article on your own ad-filled blog solely for the revenue.

Doesn't that describe slashdot pretty well?

Re:Try reading the article.

[geobeck (924637)]

Why do we tolerate it more when it's a creepy-looking Frenchman?

I've asked that question after every Gerard Depardieu movie.

Re:Try reading the article.

[Baddas (243852)]

Nice astroturf. He distills a half-page article into a half page blog post. Inaccurately.

Placing a film of silicon nanoparticles onto a silicon solar cell can boost power, reduce heat and prolong the cell's life, researchers now report.
"Integrating a high-quality film of silicon nanoparticles 1 nanometer in size directly onto silicon solar cells improves power performance by 60 percent in the ultraviolet range of the spectrum,"

Becomes

Physicists from the University of Illinois at Urbana-Champaign (UIUC) say they have improved the performance of solar cells by 60 percent. And they obtained this spectacular result by using a very simple trick. They've coated the solar cells with a film of 1-nanometer thick silicon fluorescing nanoparticles.

That's a whole 12 characters shorter, and leaves out the important words 'in the ultraviolet spectrum', which changes the meaning completely. Also, those emitted words are 27 characters long, so if they were properly included, his summary is actually more wordy than the original source.

It's almost word for word. And it's wrong.

Correction

[friedo (112163)]

The nanoparticles improve efficiency by 60% in the ultraviolet spectrum. The visible light spectrum is only nominally affected.

It's still pretty cool, though.

Re:Correction

[goldaryn (834427)]

Still pretty useful though I bet.. but:

As the alcohol evaporated, a film of closely packed nanoparticles was left firmly fastened to the solar cell.

Whoa, whoa, whoa! Back up, bad idea!




(yeah I know it's only isopropyl alcohol. but still never something you want to hear!)

Re:Correction

[phoenixwade (997892)]

As the alcohol evaporated, a film of closely packed nanoparticles was left firmly fastened to the solar cell.
Whoa, whoa, whoa! Back up, bad idea!

Why? the only issue I could see would be dumping the alcohol into the environment, but since it's evaporating off - building a recovery system into the process would save money in manufacturing, and is a no-brainer. So I'd think it very unlikely that a regular dumping of alcohol into the environment would occur, for the best of reasons from a business point of view - it's cheaper to do it the right way.

Re:Correction

[by Anonymous Coward]

Hahahahahaha. Man, you totally missed his point.

He wasn't talking about the effect it might have on the environment. He was joking about "alcohol" as in booze being left out and undrunk long enough that it evaporated.

See, in a place like Ireland it's considered near criminal to waste ale or lager. So the thought of alcohol evaporating is a disturbing thought to most Irishmen and Irishwomen. It bothers them much like the thought of global warming bothers environmentalists.

Still something

[Moraelin (679338)]

It's still something, because to knock an electron out, the minimum frequency of the photon has to be at least the difference between the conduction band (where you want that electron) and the lower-energy valence band (where the electron originally is.) So you have a minimum energy cut off point. Exactly where that is, depends on the material, but generally you won't get any power out of the infrared falling on that cell.

However, the downside is that photons with higher energy than that bandgap, well, the extra energy is essentially wasted.

So basically, say, if you used Germanium at 0.67 EV bandgap, you'd catch more photons than with Silicium at 1.11 EV bandgap, but get less useful energy (i.e., electricity as opposed to heat) out of each photon.

And the higher frequency the photon, the more you waste as heat. So you won't waste more in the visible spectrum (well, unless the photon had less energy than the bandgap, in which case it's completely wasted), but in the UV spectrum you waste a lot.

So reducing the waste in the UV spectrum is really where it counts the most. Sure, it would be neat to gain everywhere, but the UV range is where we waste the most.

Their talk about fluorescent particles, makes me think they're essentially converting an UV photon into at least one lower frequency photon. The question is what they do with the extra energy. At the simplest imaginable way, you'd get at least two low energy photons from one UV photon.

On the other hand, it seems to be a bit more than that, from that short summary linked to. From their claim that they improve voltage, not just current, and that something happens at the interface between the particles and the substrate, it sounds like essentially they created a bunch of new junctions there. I.e., that it's a new way to make a multi-junction solar cell.

Multi-junction cells aren't exactly new, but traditionally they've been very expensive so far. If these guys invented a cheap way to make one, kudos to them.

On yet another hand, it will be interesting to see on exactly what existing cells can their film be applied. On silicon or other semiconductors, ok, I can see how it would form an extra junction. Would it also work on, say, Dye-sensitized Solar Cells? There essentially their particles would come on top of the dye, and I'm not sure how well that works. It'll be interesting to find out, eventually.

Voltage

[benhocking (724439)]

So basically, say, if you used Germanium at 0.67 EV bandgap, you'd catch more photons than with Silicium at 1.11 EV bandgap, but get less useful energy (i.e., electricity as opposed to heat) out of each photon.

Can't you just increase the operating voltage to capture most of the extra energy? An electron moving across a larger voltage produces more energy. How large you can set the voltage depends on the energy in the electrons being knocked out — or am I missing something?

Re:Voltage

[mdsolar (1045926)]

In a detector you are correct but in a power device you use the doping gradient because bias voltages leak, defeating the purpose.
--
Get solar power: http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html [blogspot.com]

Silicium?

[camperdave (969942)]

Yes, you are too late to send your letter to the Prussian consulate via the 4:30 autogyro to Siam.

Re:

[speculatrix (678524)]

there's quite bit of UV in sunlight, so for photovoltaic panels which are to be used outdoors this is a real gain.

the cost of making PV panels is still too high compared to the energy you can harvest using them (I choose to use "harvest" specifically because they capture energy from the sun rather than generating from oil for example) over the expected lifetime of the panels. the other problem with PV panels is the environmental cost of manufacture + transport + ancillary electronics to make them useful an

Re:Correction

[afidel (530433)]

the cost of making PV panels is still too high compared to the energy you can harvest using them (I choose to use "harvest" specifically because they capture energy from the sun rather than generating from oil for example) over the expected lifetime of the panels.
I'm not sure if you're talking about energy cost or economic cost, but either way you are wrong. Solar panels make up their production energy cost in a fraction of their design life, and they are competitive with most non-renewables even at todays cost let alone the expected cost of those sources over the design life of the panels.

Re:Correction

[delt0r (999393)]

The total environmental cost of PV is far lower than almost anything else, and thats based on a 20 year lifetime which easily exceeded. Its pure fallacy that they are a net polluter. Problem is you need to wait 10+ years to get that net gain. Oh and consider that the energy to make the PV cell came from PV cells? Then what......

Having said that. I'm not a fan of the thin film PV that contain Cd (I don't use NiCd rechargeable's either). I know its not much, but its really nasty stuff.

Re:Correction

[hedwards (940851)]

That's correct, but what you failed to note is that the UV spectrum contains a much larger amount of energy than either the visible or the infrared spectra do. Shorter wavelength, higher energy. And the higher energy particles are the ones that are the most desirable anyways.

This 60% UV is just ONE of the configs...

[Ungrounded Lightning (62228)]

The nanoparticles improve efficiency by 60% in the ultraviolet spectrum. The visible light spectrum is only nominally affected.

It's still pretty cool, though.

This whole series of "only 60% of the UV part" threads is missing the rest of the article. That was just for ONE size of naonparticle, suitable for converting light to the middle of the visible range. They ran the tests for another size, suitable for converting to visible red, and got a higher conversion result, as expected.

Solar cells completely miss photons below the bandgap energy and only peel off the bandgap energy from those above it. They have a bandgap in the infrared so they get most photons, but only take that first 0.6 electron-volt chunk of their energy and lose the rest as heat. That's great if you have an infrared photon at 0.603 eV, not so hot for visible light photons at 1.8-3.1 eV, and pretty crummy for UV photons at 3.1 to 12 or so eV.

Films of nanoparticles have an interesting property: They absorb photons of various wavelengths and emit photons of particular wavelengths related to their size. But they don't do that in the solar-cell style of chopping the right-sized hunk off a more energetic photon and throwing the rest away. Instead they are able to combine energy from multiple lower-energy photons to generate one of the desired energy, chop several desired energy photons out of a high-energy one (and keep the leftover shavings to combine with others to make more desired-energy photons), and trade energy among their neighboring particles.

So it was expected that a film of nanoparticles on a solar cell would grab the energy from photons all over the spectrum, convert it to the energy characteristic of the nanoparticle size, and re-emit that. The improvement from efficiently salami-slicing and stacking photons should be better than losses from such things as emitting the photon in the wrong direction, giving a big boost to the cell.

And to some extent that was happening: Feed UV photons to nanoparticles that chunk 'em into something in the 3 eV range and you get more out of the UV hitting the cell than you would without the film - without appreciably affecting the output from the visible light. You're averaging about 1 2/3 IR photons worth of energy, instead of 1, for each incoming photon. Feed it to nanoparticles that chunk it up finer, down to 2 eV or so, and you get more out of your UV and also start improving on even visible light.

That's a good sign for doing what you really wanted to do: Use nanoparticles that emit just a tiny squidge above the solar-cell's bandgap, chunking all the photons into the right size for the cell and wasting very little of their energy. (But maybe still losing a bunch by emitting them in the wrong direction. That might be improved by putting the nanoparticles at the bottom of wells in the cell rather than on a flat surface.)

But the experiment produced a surprise: The VOLTAGE went up! WTF?

That means one of two things:
  a) The nanoparticles affected the bandgap.
  b) The nanoparticles coupled directly into the cell's "circuitry" in some non-obvious way.

b) might lead to something even better: Nanoparticles that capture the photons, chunk and stack them into some desired size (voltage), and deliver them directly to the wiring. That could get virtually ALL the incoming energy into your wires.

A solar cell with efficiencies in the .90s could be a whole heck of a lot better than even the experimenters were originally chasing. So it's no wonder they published now, with only two sizes of particles tested.

Hot DAMN!

Re:Correction

[Original Replica (908688)]

9.6%! Nothing to write home about.

As gas prices creep ever higher and coal plants become less and less desirable a partial conversion to solar power starts to become a very possible reality. Adding just one kilowatt worth of solar power to each of America's 116 million homes would reduce the power consumption almost 1/3rd. http://www.frugalfun.com/solarfest.html [frugalfun.com] The system to get "off the grid" discussed my link costs a fair amount of money, and even a 1 KW system costs $10,000 right now, but if the solar panels can suddenly cost 60% less (by being more efficient) then the price of a 1 KW system could reasonably drop to $5000. Not a huge cost when you are talking about much of todays housing market. Five grand is less than the price difference between a Prius (22K) and a Ford Focus (15K). Solar might well become widespread after all, not because it is efficient, but because everything else is slowly rising to match solar power's high initial cost.

TiO2, UV, and Solar Cubes

[purduephotog (218304)]

While at Purdue one of my friends worked on a process to increase solar cell efficiency by etching TiO2 coatings into long, thin whiskers that helped 'whisk' photons down into the surface of the material. It basically doubled the efficiency of a 3% cell in the visible range. Solar hasn't taken off.

Glass typically blocks UV. Most glazings contain glass. If this only boosts (and 60%, while a large number, is still a tiny increment in efficiency) the UV efficiency then there may be limited use... unless you count concentrator applications.

The "Sun Cube" (http://www.treehugger.com/files/2007/04/sun_cube_ by_gre_1.php [treehugger.com] uses lenses to concentrate light onto small, very efficient space-grade solar panels. Each panel (if memory serves) was on the order of 1 sqcm, allowing these very expensive but very efficient (25%+) panels to be used. The overall effect was to to take 1 m2 down to 10 sqcm of chips.. and yet have the power output be about the same. Combine that concentrator technology with higher utilization of UV bands AND ultra-efficient space grade panels and you've got a winner (concentrators work ONLY in direct sun- no clouds).

Just some food for thought.

60% more than ~0 is hardly very much

[Chalex (71702)]

So I RTFA, and here's the bit: "improves power performance by 60 percent in the ultraviolet range of the spectrum" and "in conventional solar cells, ultraviolet light is either filtered out or absorbed by the silicon and converted into potentially damaging heat, not electricity."

So a conventional solar cell gets ~0 energy from this part of the spectrum, but if you coat it with this special coating, it gets 60% more! And how much is that exactly?

Now if you use a different coating (2.85nm), then it improves performance "in the visible part of the spectrum" by 10%. How much energy does a conventional solar cell get from just the visible part of the spectrum? Unspecified!

Cost

[grassy_knoll (412409)]

The process of coating solar cells with silicon nanoparticles could be easily incorporated into the manufacturing process with little additional cost, Nayfeh said.

How about something to make solar cheaper to purchase, so that the initial investment can be recouped before the expected replacement date?

Seems best suited for non-terrestrial uses

[Shadowlore (10860)]

First, we need to be careful here. A 60% improvement in the conversion among UV spectrum does not necessarily equate to a 60% increase in a given PV cell. If the particular cell is more of an infrared or visible light spectrum oriented cell, you'll see a minor, if any, improvement. So before anyone starts grabbing random solar cell outputs and starts applying a 60% increase in power and get modded "insightful" for bad information, let's get that part out there.;)

With the main advantage being in the UV spectrum, it seems to me the best application would be to UV preferential cells in orbit or on Mars, Luna, etc.. Doubly so given the difficulty in shedding excess heat in Space.