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Nanotechnology Boosts Solar Cell Performance

Posted by ryuzaki0 on from the two-great-tastes dept.

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."

12 of 176 comments (clear)

  1. Correction by friedo · · Score: 5, Informative

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

    It's still pretty cool, though.

    1. Re:Correction by speculatrix · · Score: 2, Informative

      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 and the cost of disposing/recycling. whether photovoltaics will reach the desired efficiency to make them economically and environmentally cost effective before biological (algae, bacteria etc which can "generate" methane or hydrogen for fuel) systems are perfected is an interesting question.

    2. Re:Correction by m4cph1sto · · Score: 2, Informative

      This is incorrect. UV radiation is of higher energy, but much lower intensity than light in the visible range, so overall much less energy is extracted from UV, and improving UV efficiency is not a big deal. The technological challenge in the development of photovoltaic materials is to develop a system that works efficiently in the visible range.

    3. Re:Correction by afidel · · Score: 4, Informative

      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.

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    4. Re:Correction by Eponymous+Bastard · · Score: 2, Informative

      The technological challenge in the development of photovoltaic materials is to develop a system that works efficiently in the visible range. That depends on your application. Residential solar power might not be affected as much by this improvement, but space applications are.

      Satellites dont have an ozone layer filtering UV light. They even get light in the UVC range (you know those UVA+UVB sunscreens? there's no UVC sunscreen except for NASA) so the 60% improvement is probably a big number, I'd have to calculate it. Making satellites with smaller panels with a thin film of particles is probably cost effective right away, given current launch costs. Additionally, the article mentions this decreases heating as well, which is probably a good thing in direct sunlight.

      Any rocket scientists out there care to comment?

      Also note that this is improvement is orthogonal to any improvement in visible light absorption. In fact, future improvements in visible light would translate into an improvement in UV with this method.
  2. Re:Try reading the article. by Baddas · · Score: 5, Informative

    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.

  3. Still something by Moraelin · · Score: 5, Informative

    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.

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  4. Re:Try reading the article. by Baddas · · Score: 4, Informative
    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.

  5. Re:Voltage by mdsolar · · Score: 3, Informative

    In a detector you are correct but in a power device you use the doping gradient because bias voltages leak, defeating the purpose.
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  6. Silicon Nanoparticles by GravitonMan · · Score: 3, Informative

    At the end of the blog Roland asked why they didnt use multiple sizes of silicon nanoparticles, this was my long winded reply:

    I am a graduate student working on the synthesis of silicon nanoparticles for solar cells and other applications. While silicon nanoparticles have been syntheszed for over 20 years, and their are many ways of synthesizing them, it is still very difficult to control the size of the particles. Unlike CdSe based quantum dots where the size of the particles is determined by how long your let the reaction run for, 1 min for blue 30 min for red, and various time lengths for other colors, silicon nanoparticles are more complex.

    Silicon nanopariticles while they are still quantum dots, since the energy levels are somewhat quantized emit very differently as well. Silicon is an indirect band gap semiconductor, however the blue emitting silicon nanoparticles emit light with a direct band gap transisiton, where as they red emitting silicon nanoparticles are controlled by more surface effects and emit in a low energy indirect band gap transition which is slower and allows for more energy loss in other modes.

    Anyways, what it comes down to, is it is difficult to make various sizes of silicon nanoparticles. I would also like to add that this technique is not very promissing for several reasons, they epense and other problems with traditional silicon etched solar cells still exist. Cost, lack of flexibility, low effeciency, heavy, glass... This method does not take full advantage of multiple exciton generation which was just proved for silicon nanoparticles in ACS journal of Nano Letters this week. PbSe quamtum dots have shown to generate 7 exciton for just one photon, which in theory could be converted to 7 electrons from 1 photon...someday. But 2.6 excitons from silicon nanoparticles is still pretty good. Especially when I have a way to get the excitons into free electrons And silicon is a non-toxic cheaper alternative to the PbSe quantum dots.

  7. Re:Another breakthrough.. by mdsolar · · Score: 2, Informative

    The AC has a point though that slashdot does not do a lot of followup. For example this 2005 article: http://science.slashdot.org/article.pl?sid=05/02/2 8/1224245 has not really had a follow up to say that they have products on the market now: http://www.nanosolar.com/products.htm, or that this 2004 article: http://science.slashdot.org/article.pl?sid=04/10/2 2/1534212 about solar shingles is also seeing application in new housing now. Looking back, there are articles on ideas that have not panned out so far, especially in organic solar technology. But, that does not mean that they won't.
    --
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  8. Re:Cost by dbIII · · Score: 2, Informative

    Why don't you just post more recent information instead of telling the OP that they're ignorant?

    OK. Zone refining of silicon is done in large quantities now at much lower energy usage and cost than before and the high qualitity single crystal silicon ingots are cut into large wafers that are used to make things like microprocessors and solar cells. Thanks to the huge demand for semiconductors silicon solar cells are nowhere near as expensive as they were in the 1960's. There are some that are not made that way and they are still expensive.

    Is that enough to address an argument that is thirty years out of date?