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Science Technology

Research Promises Full-Spectrum Solar Cell 67

Posted by timothy from the recycle-your-glow-sticks dept.
nphillips writes "As is being here reported here, a serendipitous discovery was made that a single system of alloys incorporating indium, gallium, and nitrogen can convert virtually the full spectrum of sunlight -- from the near infrared to the far ultraviolet -- to electrical current. For if solar cells can be made with this alloy, they promise to be rugged, relatively inexpensive -- and the most efficient ever created. Solar cells so efficient and so relatively cheap could revolutionize the use of solar power not just in space but on Earth."
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Research Promises Full-Spectrum Solar Cell More

Research Promises Full-Spectrum Solar Cell

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  • Damn, I came up with this idea when I was 12 years old. There go my retirement plans...

    As I understand it, UV light hits the earth at all hours.

    Does anyone know how much UV hits the earth during the night? If there's more then a trivial amount of light at night, it means that these new solar panels could potentially generate electricity 24 hours a day.

    Even if the nighttime energy generation is 1% of the daytime energy generation, it's still a great improvement over today's solar panels.
    • As I understand it, UV light hits the earth at all hours.

      UV or IR? I've never head of UV light reaching the dark side of the planet in any quantity (other than whatever light you get from stars & off the moon). IR (mostly thermal energy) is usually quite abundant, though.

      Got any references?
      =Smidge=

    • Re:UV during nighttime... (Score:5, Informative)

      by Christopher Thomas ( 11717 ) on Monday November 18, 2002 @02:34PM (#4699823)
      As I understand it, UV light hits the earth at all hours.

      Does anyone know how much UV hits the earth during the night?

      Almost none. Virtually all of the light that strikes Earth comes from the sun.

      As another poster pointed out, you may be confusing this with the mid-IR glow that warm objects (including the ground and the air) give off. The amounts of energy involved are very low, and room-temperature thermal IR is difficult to convert to electricity efficiently.

      Any solar power scheme (and so any photovoltaic scheme) has to have enough storage capacity to power the load overnight. Ideally, it should be able to provide power for several days, in case of cloud cover/rain/whatever. This is why most home-powering schemes involve large battery arrays. A city-powering solar plant would probably use fuel cells (energy density is much higher, and there are off-the-shelf models of power-plant scale already available and in use).
      • Just a thought. I wonder if it's reasonable to pump water to elevated storage and use this as overnight power. Overnight power needs are MUCH less than peak day time needs. This discrepency could take care of the energy losses in the pumping schema. With a very efficient solar cell we might not mind the loss of energy being redirected to water pumping. An added side benefit: aerating water helps remove organics (foam fractionation). Now if we had a million solar roofs and elevated water tanks... Admittedly this solution is awfully dependant on availability of water and space. Anyone for flywheel batteries?
        • Just a thought. I wonder if it's reasonable to pump water to elevated storage and use this as overnight power. Overnight power needs are MUCH less than peak day time needs.

          You could, but energy density is extremely low (a few tens of joules per kilogram for something you could install in your backyard, vs. tens of megajoules per kilogram for fuel cells or hundreds of kilojoules per kilogram for batteries). The plumbing and storage itself is cheap, but the pump/generator will probably cost more than batteries and a power converter would.
    • Does anyone know how much UV hits the earth during the night?

      Not much unless there is a nearby supernova or something. The star Betleguise (sp?) in the Orion frame is due to blow up any time now. However, I wouldn't design your power cell arragements around such assumptions. The estimations are possibly off by a few million years.

  • Wow. (Score:3, Insightful)

    by Unknown Poltroon ( 31628 ) <unknown_poltroon1sp@myahoo.com> on Monday November 18, 2002 @01:05PM (#4698799)
    Better than 70% efficency, versus 25% for current solar cells. Ok, now im willing to accept solar might be feasable.

    • Re:Wow. (Score:3, Interesting)

      by bjn ( 168572 )
      Efficency's not the main reason for the slow uptake of PVs as a viable alternative, it's the capital cost per unit energy generated is the problem.

      Currently roof space is cheap, solar cells aren't. The big step is getting $/W down, not the W/m^2 up.

      That said, ideally you want low cost _and_ high efficiency.
      • ok, that makes sense, but in the past, as i understand it, to get a decent amount of power out of solar cells, youd have to plate over, say austrailia. Now you just have to plate over, half of austraila. What the hell, hats a major improvement.
        • ...Now you just have to plate over, half of australia. What the hell, thats a major improvement.


          Umm... what, exactly, would be improved by plating over half of Australia? And which half would be an improvement?



          Careful how you answer; some Aussies read slashdot, too.

  • A new definition for (Score:4, Funny)

    by Froze ( 398171 ) on Monday November 18, 2002 @01:09PM (#4698848)
    vaporware!

    and I quote
    "In MBE the components are deposited as pure gases in high vacuum at moderate temperatures under clean conditions."

    Further
    "If it works, the cost should be on the same order of magnitude as traffic lights," Walukiewicz says. "Maybe less." Solar cells so efficient and so relatively cheap could revolutionize the use of solar power not just in space but on Earth."

  • Orbital Manufacture (Score:3, Informative)

    by Euphonious Coward ( 189818 ) on Monday November 18, 2002 @01:29PM (#4699060)
    This could be really important if the carrier lifetime really is long enough to get power out of the cell without covering most of it with the mesh of metal wires.

    What the article didn't mention is that this material could be the killer app for orbital manufacturing. The value of the cells would justify lofting the raw metals into space to form into enormous panels in the open vacuum, free of contaminants. Solar cells with 50% efficiency would compete economically against fossil fuels.

    • Re:Orbital Manufacture - REALITY CHECK (Score:5, Insightful)

      by 0x69 ( 580798 ) on Monday November 18, 2002 @03:45PM (#4700609) Journal
      The article noted that current-best solar cells are about 25% efficient, vs. 30% max. theoretical. How many percent more efficient are you figuring on the new solar cells being if space-made (vs. Earth-made)?

      Check out the $billions$ that the dinky space station costs just to keep up. Ditto launch costs for your raw materials & totally unproven zero-grav solar cell factory equipment.

      Now spread the extra costs of space-made solar cells out over the number of cells that you think will actually pass QC & reentry. Where do you see the high-volume market willing to pay the $HUGE$ price premium for a few percent better efficiency?

      As gbell notes further down, efficiency doesn't mean too much, especially competing against fossil fuels. Cost per watt (call it financial efficiency) is what really matters.

      • Re:Orbital Manufacture - REALITY CHECK (Score:1)

        by Anonymous Coward
        30% max theo. is with the silicon chips in a narrow spectrum. This is wide spectrum and slightly different material.
      • The article noted that current-best solar cells are about 25% efficient, vs. 30% max. theoretical. How many percent more efficient are you figuring on the new solar cells being if space-made (vs. Earth-made)?

        RTFA. 30% is max efficiency for single-layer cells. Multi-layered cells can get up to 75%.

        Now spread the extra costs of space-made solar cells out over the number of cells that you think will actually pass QC & reentry. Where do you see the high-volume market willing to pay the $HUGE$ price premium for a few percent better efficiency?

        I thought the original poster was talking about manufacturing panels in space, for use in space.

        As gbell notes further down, efficiency doesn't mean too much, especially competing against fossil fuels. Cost per watt (call it financial efficiency) is what really matters.

        True, but unless the cost of manufacture scales up faster than the efficiency, this is a win by both criteria.

        • I read the article...you're missing my point. It doesn't matter if the new cells can get 95% efficient - i'm looking at the SPREAD in efficiency between "Made on Earth" and "Made in Space" cells. There is just plain NO WAY that "Made in Space"'s small efficiency boost can justify the MUCH larger cost of manufacture in orbit.

          Making panels in space for use in space is interesting...but hard to reconcile with his comment about competing with fossil fuels. Burning fossil fuels for electricity in space has been rather unpopular & uneconomical for quite a few years now.

          I don't think this is about (cool idea) large-scale generation of electricity in space to be beamed down to Earth. Nothing i've seen suggests that efficiency of full-spectrum solar cells has anything to do with why that idea isn't flying.
      • If efficiency becomes a problem, couldn't we simply put the panels into a low solar orbit, failing that, antimatter is the way of the future, 100% efficency.
  • When the article mentioned being able to absorb near infrared light, I was reminded of my ridiculous idea to violate the laws of thermodynamics. Basically, you would need a solar cell that would generate power from infrared light. Use this solar cell to power a battery recharging unit. Place an uncharged battery into the unit, and put it in a dark closet for a year. At room temperature, objects should be giving off black body radiation in the infrared spectrum, so the wall of the closet should be emitting trace amounts of infrared light. So, with enough time, the trickle of current should recharge the battery. Therefore, I have taken heat energy, which is very entropic, and confined it to a battery, thereby decreasing the entropy of the system without expending energy to do it. I know this can't work, but I'm having trouble seeing why. Any ideas?
    • You're still converting one form of energy into another. That infrared would otherwise be radiating to other objects, increasing their entropy. The infrared produced is tiny compared to the total entropy of the object radiating it, so you could look at it as absorbing the small amount of spontaneous order generated from chaos.

      In addition, as I said in the subject, light is light. If one frequency of light can be turned into energy, they all ought to be susceptible to the same concept, if not the same receiver.

      Here's a question for you, and for everyone else: Would a solar cell continue to operate in an ambient temperature sufficient to generate that frequency in black-body radiation?
      • Here's a question for you, and for everyone else: Would a solar cell continue to operate in an ambient temperature sufficient to generate that frequency in black-body radiation?

        I *think* the answer is "no", as thermal energy would cause current to flow both ways across the junction you're trying to use to generate power, but as this is not my area of expertise, I could easily be wrong.
        • BUT, it is supposed to be possible to create a 'diode' for heat by using certain non-linear materials (apparently, things like DNA). Of course, if you're just referring to electricity flowing both ways, that's easily solved by a simple semiconductor junction.
          • Of course, if you're just referring to electricity flowing both ways, that's easily solved by a simple semiconductor junction.

            Apparently you didn't read my message.

            When the thermal energy of carriers within the diode is much greater than that imbued by the voltage drop across it, the junction conducts in both directions. Diodes stop working when they get too hot.
      • Um. Yes. It would. I think. As long as the level of incoming light exceeds the level of the black-body radiation (which is probably very low). I don't think that the black-body radiation is really relevant to the physics of the situation.

        However, if you're hot enough for there to be a meaningful amount of black-body radiation in the visible range where many solar cells operate, you're probably hot enough to damage the solar cell anyway.

      • This is an interesting twist on the subject!

        The answer is no, as suggested by the Second Law. To see why, you need an account of how solar cells actually work.

        Infalling light is absorbed by the material, by dislodging electrons either from a bound orbit, or a semi-free state like a metallic subtrate or semiconductor. The electron absorbs the photon, re-emitting some of the light as another, lower frequency photon, and taking some of the the momentum and energy with it. The new energy and momentum is sufficient to transport it over a potential barrier to the other side of a layered semiconductor or similar. (All semiconductors are layered -- typically they upper few micrometers are doped, wheras lower down it has a different composition).

        The solar cell's composition is such that the electron moves up a potential hill, over the brow, and sits in a dip at the top (on the other side of the solar cell). From there, it can get down the hill again (lose it's energy) either by getting over the brow again, or by travelling down the handy attached wires and charging a battery (say).

        Imagine if the back of the cell was transparent, and also exposed to sunlight: Then the sunlight falling on that side would knock electrons down the hill as well! This would actually happen EVEN MORE because the work needed to get over the brow out of the little dip at the top is much smaller than the work needed to get all the way up the hill. The difference is that you can't make the electron do any useful work if it is already at the bottom of the hill.

        Now if the solar cell is at the same temperature as the black body radiation, the (usually metal or glass) substrate on which the cell is mounted will emit black body radiation too. By the same argument, the equal amount of infalling light from the back of the cell will result in at least as many electrons being knocked down the hill as are being knocked up the hill by the infalling light you want to do the work.

        Upshot: The back of the solar cell must be cooler than the temperature of the infalling radiation for it to work.

        To clear up a last couple of points: If the back of the cell is not a black-body emitter, it will either be partially transparent or partially reflective or both. There are no other alternatives (because of the quantum symmetries involved). If it is partially transparent, then the temperature of the objects behind the solar cell becomes relevant. If it is partially reflective, the difference is made up by the reflected heat not absorbed by the solar cell -- including the black body radiation of the cell semiconductor if it is not transparent, or the infalling light if it is.

    • Because it's not a closed system. You're getting energy out of the earth's atmosphere and/or your house's heating system. Yes, that energy *is* gone. It's a teriffically tiny amount compared to the total amount of heat energy stored in even your walls, nevermind the atmosphere, but it's still gone.

      The infrared energy emitted by the walls would normally hit one of the other walls and be absorbed, only to be emitted again. When it hits your solar panel, it's absorbed, but not emitted again. You may not think of a solar panel as a cooling device, but in fact it is, if it's turning infrared energy into electricity. It's absorbing the heat your walls emit and putting it into the battery. Given a completely sealed system, that closet would eventually cool off to the point where you would stop getting any energy out of it.

      At least, that's my understanding. But hey, I could be wrong.
    • When the article mentioned being able to absorb near infrared light, I was reminded of my ridiculous idea to violate the laws of thermodynamics.

      You must have the Enron gene ;-)

  • Full Spec Solar (Score:2, Interesting)

    by guinie1 ( 537902 )
    Question: How do you make President Bush and his "real" constituency soil their adult diapers? Answer: Have them read the article! To the article authors: Hire some body guards! BTW: You have to wonder how much energy (initially) it would require to manufacture, say, a modest 100 kW solar power plant and the amounts of pollution that manufacturing process would produce. I guess, eventually, with enough solar power plants humming away, providing enough energy to manufacture other solar power plants, this question would be academic.
    • The ecconomic payback for a panel is generally in the 10-30 year range. The cost of a panel reflects the cost of materials and the cost of production which of course includes the cost of the electricty used for that production.

      Foccusing only on the energy used, I think Homepower.com had an article saying the energy payback was something liek 3-5 years.

  • Don't get hung up on efficiency (Score:4, Insightful)

    by gbell ( 84505 ) on Monday November 18, 2002 @03:31PM (#4700453)
    For utility/residential applications, efficiency isn't very important since there's LOTS of roof area... you can use relatively inefficient technology. What really matters is $/Watt. How much do I have to spend to generate energy equivalent my house's usage?

    ~gb



    • Gallium is currently around $640/Kg

      Indium is about $147/Kg

      Nitrogen, as far as I know, can be obtained quite cheaply.

      For comparison, silicon is about $1/Kg

      commodity info [usgs.gov]

      • Liquid nitrogen is frequently made out of air. So, yeah, nitrogen can be obtained kinda cheaply. Breathe. There you go.

        This is also why superconductors which could work at nitrogen's liquification temperature or above are such a potentially great thing. Otherwise, you're dealing with much more expensive cooling.
        • This is also why superconductors which could work at nitrogen's liquification temperature or above are such a potentially great thing. Otherwise, you're dealing with much more expensive cooling.

          Come again? What does the ubiquity of nitrogen have to do with issues about temperatures for semiconductors? Liquid hydrogen isn't expensive because hydrogen is hard to come by, you know. It's the refrigeration technique, not the medium, that costs so much.

          • What does the ubiquity of nitrogen have to do with issues about temperatures for semiconductors?

            Easy: Refrigeration is usually achieved by using a phase change because phase changes embody a rather large energy gradient; this means that you can't cool (much) below the tempurature of fusion of your given refrigerant. Liquid nitrogen is cheap, so if you have a superconductor that runs at 100K or whatever, you can operate it very cheaply.

      • I guess it all depends on how much you need and how long you will use it. For powering a house you might not need a large amount of material, and it is a one-shot deal (unless it breaks, of course). After the cost of installation, all that matters is how much energy you can get out of it in a set amount of time.

        If it is more efficient then you need less material, so the costs are a little bit less again. But someone smarter than me should do the math. I wouldn't be surprised if you would have to run the panels for 84 years before the gap was bridged, but maybe not :-)

    • it works OK if you live in suburbia but for those who live in apartments or work in multilevel offices this could provide energy for us too. a 2 story office building will consume more power per square foot than a house (more electronics, lights always on, plus air conditioning) and the office has less roof space compared to the house.

      also, there are plenty of other uses that would benefit form efficiency like cars, cameras, boats, etc.
      • a 2 story office building will consume more power per square foot than a house (more electronics, lights always on, plus air conditioning) and the office has less roof space compared to the house.

        Better use of mirrors/fiber and windows could reduce the need for electric lights and fan ventilation.

        It seems kind of dumb and wasteful to convert light to electricity and then back to light again.
        • true, better use of existing light is good for future development but many existing buildings can't easily take advantage of light this way (using mirrors and fiber optics). for those older buildings i think it would make sense to at least suppliment the 'grid electricity' with electricity produced on-site in a minimally polluting way.
  • I wonder if this material would work well with the previously mentioned Spheral Solar technology people?

    http://www.spheralsolar.com/

    If the absorbtion range is as good as they said, then one would hope the same method could be used... I guess it is more an issue of the InGaN actually forming spheres.

  • What about the rest of the EM spectrum. If electricity could be gotten from that, it would be even better.
    • What about the rest of the EM spectrum. If electricity could be gotten from that, it would be even better.

      Not by much. Most of the energy emitted by a hot object is near the peak of the black-body curve. The sun's surface is hot enough to put this well into the visible range (and enough of it beyond that range to give beachgoers a nasty sunburn). If you can process everything from near-IR to near-UV (or farther), you've got almost all of it.
    • We already get electricity from the radio region of the spectrum. Radio waves fly by and move electrons in an antenna and attached wire. The wire leads into an amplifier and a few nifty transistors, and voila, you have Car Talk with Click & Clack (NPR) telling you how to fix that busted alternator.
    • What about the rest of the EM spectrum.

      It seems the lower end is harder to get energy from because it is rather whimpy energy relative to light. And, the higher end is fortunately mostly filtered out by our atmosphere and magnetosphere, otherwise we wouldn't live very long.

      Thus, we are pretty much stuck in the middle.

      I don't know if something outside of Earth's magnetosphere could effectively harness higher-end radiation. High-end radiation tends to damage the very devices used to harness it.
  • someone from the oil and gas industry offers an ungodly sum of money to buy all the tech and research associated with it and then shit cans the whole thing.
  • The first clue to an easier and better route came when Walukiewicz and his colleagues were studying the opposite problem -- not how semiconductors absorb light to create electrical power, but how they use electricity to emit light.

    Heinlein described in one of his short stories how some guy using nano-crystals to create the ultimate "cold light source" and noticing that, like most physical processes, this one is works in reverse as well - he's just invented the "perfect" solar collector! Of course the technical specifics are wrong, he got even them pretty close, and he got the basic idea right...

    I also loved how he threw in "small" inventions with thought-out consequences into his stories as background. There's a scene I'll always remember where a young cadet-wannabe facing testing answers his father's call on the cell phone while his friend smirks "I tricked my parents - packed the phone in my bags". I bet this scene is replayed with variants all over the world by now. Pretty good for a story written in the 50s or 60s.

    Now, where's my budget rental spaceship he was so derogatory about?

    • Re:Old stuff - Heinlein "invented" it years ago :- (Score:4, Interesting)

      by Tumbleweed ( 3706 ) on Monday November 18, 2002 @06:52PM (#4702344)
      I don't know if that's the same story or not, but I was remembering one where two scientists invent a full-spectrum solar cell, and the only way they can get it into the world without getting themselves murdered first, is to publish the specs openly and then collect royalties.

      Heinlein - he da man! :)

      As an aside, a much more feasible way of vastly reducing our dependency on fossil fuels would be to switch everything feasible over to biodiesel. A lot less pollution, too, as well as better fuel efficiency than gasoline engines, plus the engines are simpler and last longer than gasoline engines (no spark system - diesel engines ignite during the compression process - no spark plugs, etc. needed).

      Do a Google search for 'biodiesel' and enlighten yourself.


    • This is exactly what I thought about when I read this thread. The story is,Let There Be Light, and it featured two scientists (a man and woman) working to create and implement this technology ahead of those from the "power cratels" that wanted to stop them.



      This is one of the "earliest" stories in his future history series and forms the basis for much of that history. His story The Roads Must Roll builds on this technology as the power source for his "rolling roads". For a full listing of his short fiction and how it fits together, check out this great site [nitrosyncretic.com], which appears to be the best Heinlein site on the web.

  • The big advantage of these cells is that right now a large portion of the suns rays hits our solar panels and efectively bounces off. maybe all the stuff in the infrared and most of the uv. These because they effectivly have a broader frequency response can soak up a larger portion of the energy falling on them.
    • current commericial solar cell designs actually absorb a large frequency range of the sun's EM energy; little is reflected unless the angle of incidence is oblique enough. the issue is that only a certain frequency range can push electrons into the conduction layer of the material (i.e. produce electricity). the remainder of this absorbed energy will mostly increase the amount of heat in the material. this heat will either be conducted away or be re-radiated as longer wavelength photons.

  • Tungsten (Score:3, Interesting)

    by Catskul ( 323619 ) on Monday November 18, 2002 @07:00PM (#4702401) Homepage


    There was article a little while ago about how they had created a new tungston crystal configuration that would adsorb radiation in a certain spectrum and re-emitt at another. In that case they were adsorbing infrared and re-emitting at visible to wildly increase the efficency of incandencent lights, but IIRC the article said that it could be tuned to a wide range of spectra.

    What is keeping them from using this to adsorb the visible spectrum and re-emit at an effecient spectrum from converting to electricity ?

  • Defect Densities, People... (Score:4, Informative)

    by clark625 ( 308380 ) <clark625 AT yahoo DOT com> on Monday November 18, 2002 @10:41PM (#4703468) Homepage

    What the article doesn't happen to mention is that InAs (Indium Arsenide) was believed to have a bandgap around 1.6eV (not sure the exact number) and it's now known to be somewhere in the range of ~0.6eV. The article also don't mention phosphide compounds, which are far bigger in research and industry right now.


    Fact is, nitrides are bastards to grow. You have to use gas-sources (instead of solid sources that most MBE-ers prefer). There's also no current way to make a nitride-based substrate, which means growing (typically) on sapphire or other lattice mis-matched substrates (GaAs, InP, etc). These lead to HUGE dislocation densities that greatly impact performace.


    Now, that doesn't mean this can't be done. And in fact, magic is being done all the time in the world of research. But nitrides aren't going to be realized for some time. Not at least until other technologies pan out first (phosphides and the like). Those are cheaper to grow and allow for much lower defect densities.


    Just so you folk's know I'm not just talking out of my ars--do some research and look up some papers. Authors to look for are Steve Ringel (OSU), Gene Fitzgerald (MIT), John Carlin (OSU), Sumitomo (Japan, somewhere), and by-far Yamaguchi (Toyota Technological Institute). Read up on these folks' work and those around them--they know space-based photovoltaics better than most, and very, very, very, very few are working with nitrides right now. Not that it's not going to eventually happen--but until defect densities get low enough, there's simply no way to make a good solar cell (read up on the previous authors' works if you want the theoretical calculations as to why).

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