Oh the horror! Carbon based semiconductor solar cells

OK, so the headline is tongue in cheek, but Halloween is coming soon. As much as everyone want to demonize Carbon, I find this finding interesting for it’s uniqueness and timeliness.

Rutgers discovery paves way for development of efficient, inexpensive plastic solar cells

Finding reported in Nature Materials journal could boost role of solar-generated electricity as alternative to fossil fuels

NEW BRUNSWICK, N.J. – Physicists at Rutgers University have discovered new properties in a material that could result in efficient and inexpensive plastic solar cells for pollution-free electricity production.

The discovery, posted online and slated for publication in an upcoming issue of the journal Nature Materials, reveals that energy-carrying particles generated by packets of light can travel on the order of a thousand times farther in organic (carbon-based) semiconductors than scientists previously observed. This boosts scientists’ hopes that solar cells based on this budding technology may one day overtake silicon solar cells in cost and performance, thereby increasing the practicality of solar-generated electricity as an alternate energy source to fossil fuels.

“Organic semiconductors are promising for solar cells and other uses, such as video displays, because they can be fabricated in large plastic sheets,” said Vitaly Podzorov, assistant professor of Physics at Rutgers. “But their limited photo-voltaic conversion efficiency has held them back. We expect our discovery to stimulate further development and progress.”

Podzorov and his colleagues observed that excitons – particles that form when semiconducting materials absorb photons, or light particles – can travel a thousand times farther in an extremely pure crystal organic semiconductor called rubrene. Until now, excitons were typically observed to travel less than 20 nanometers – billionths of a meter – in organic semiconductors.

“This is the first time we observed excitons migrating a few microns,” said Podzorov, noting that they measured diffusion lengths from two to eight microns, or millionths of a meter. This is similar to exciton diffusion in inorganic solar cell materials such as silicon and gallium arsenide.

“Once the exciton diffusion distance becomes comparable to the light absorption length, you can collect most of the sunlight for energy conversion,” he said.

Excitons are particle-like entities consisting of an electron and an electron hole (a positive charge attributed to the absence of an electron). They can generate a photo-voltage when they hit a semiconductor boundary or junction, and the electrons move to one side and the holes move to the other side of the junction. If excitons diffuse only tens of nanometers, only those closest to the junctions or boundaries generate photo-voltage. This accounts for the low electrical conversion efficiencies in today’s organic solar cells.

“Now we lose 99 percent of the sunlight,” Podzorov noted.

While the extremely pure rubrene crystals fabricated by the Rutgers physicists are suitable only for laboratory research at this time, the research shows that the exciton diffusion bottleneck is not an intrinsic limitation of organic semiconductors. Continuing development could result in more efficient and manufacturable materials.

The scientists discovered that excitons in their rubrene crystals behaved more like the excitons observed in inorganic crystals – a delocalized form known as Wannier-Mott, or WM, excitons. Scientists previously believed that only the more localized form of excitons, called Frenkel excitons, were present in organic semiconductors. WM excitons move more rapidly through crystal lattices, resulting in better opto-electronic properties.

Podzorov noted that the research also produced a new methodology of measuring excitons based on optical spectroscopy. Since excitons are not charged, they are hard to measure using conventional methods. The researchers developed a technique called polarization resolved photocurrent spectroscopy, which dissociates excitons at the crystal’s surface and reveals a large photocurrent. The technique should be applicable to other materials, Podzorov claims.

###

Collaborating with Podzorov on the research were postdoctoral researcher Hikmat Najafov, graduate students Bumsu Lee and Qibin Zhou, and Leonard Feldman, director of the Rutgers Institute for Advanced Materials, Devices and Nanotechnology (IAMDN). Najafov and Podzorov are also affiliated with IAMDN.

Funding was provided by the National Science Foundation’s Division of Materials Research and Japan’s New Energy and Industrial Technology Development Organization (NEDO).

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42 thoughts on “Oh the horror! Carbon based semiconductor solar cells

  1. Hi Folks!
    HAPPY CLIMATE FOOLS DAY!
    To commemorate the 10:10 eco-snuff movie, I would like to suggest that October 10 henceforth be celebrated worldwide as Climate Fools Day.
    Let this day forever be a reminder of how the eco-fascists blew themselves up with their own hateful propaganda, marking the beginning of the end of the global warming scam.
    Can our internet-savvy friends please help create a website–something along the lines of “climatefools.org”–with links to the 10:10 eco-snuff movie. The objective is to shame these green bullies and remind them that civilized people won’t tolerate their unacceptable fascist behavior.
    e.g. text on website page:
    —————————–
    -Ticking countdown- LEFT TO CLIMATE FOOLS DAY!
    CLIMATE FOOLS DAY is a day of peace and sanity where the free peoples of the world celebrate:
    – The end of eco-fascism
    – Electricity and all its life-enriching benefits
    – Oil and coal and all their life-enriching benefits
    – Cows and all their tasty benefits
    – All the good things about protecting and caring for our environment, minus the fraud that is carbon taxation, emissions trading, biofuels and other unproven renewable energy technologies
    But No Pressure!
    LESS WE FORGET
    – 10:10 eco-snuff video
    – Franny Armstrong’s Half-assed Hahaha Apology
    – 10:10’s follow-up whiny “I just got a baby” apology
    – Sony statement
    – Kyocera statement
    – Mind-boggling hypocritical statement by 350.org’s Bill McKibben, condemning the 10:10 movie while calling those who question the science of global warming “deniers”
    —————————–

  2. Nice to see that some people are still doing science not based on computer models. One day this “might” be practical and affordable technology.
    For now, we need “fossil” fuels and nuclear.

  3. Maybe we should get billions in research funds to figure out the most expensive way to convert CO2 in the atmosphere into rubrene. Kill two birds with one stone, make a fortune, all while consuming far more resources than the product could ever hope to counter, but it would sound so green they could not refuse it.

  4. ‘Tis only fitting that carbon serve Carbon-based life forms.
    The Stuff of Life. Carl Sagan would have been stoked.

  5. Maybe they should get together with the 2 University of Manchester scientists Andre Geim and Konstantin Novaselov who won the Nobel prize for Physics with a carbon compound called Graphene. They found it when they used sticky tape to get one atom thick layers from a pencil. Its potential uses seem very promising faster semiconductors that can take more heat and power than silicon.
    http://www.telegraph.co.uk/science/science-news/8043355/Nobel-Prize-for-Physics-won-by-Andre-Geim-and-Konstantin-Novoselov.html

  6. Sounds nice but things like this rarely ever come to fruition. I would like to be proven wrong though.

  7. Not to mention the importance of carbon nanotubes etc. Carbon is an extremely important element, not pollution.

  8. Let us hope that such developments can yield better pricing than this below, advertised in an automatically generated link here in the UK.
    Solar Electricitywww.tec-consultants.net
    1.6KW £6,670 installed MCS cert. 2KW £8,350 anywhere in the UK
    The price is horrendous for a system that is out of action for half the time (unless sited under a street lamp). Personally, I shall not consume £8,350 of electricity during the rest of my life.
    A much more cost effective scheme to have complete independence would be a Straight Vegetable Oil fueled diesel generator, smart inverter & a few batteries. Leisure boating technology, in fact.

  9. Still in the lab and quite a ways from practical use, but looks to be an important breakthrough. I do think solar has some good potential and it’s great to see some good practical science being done.

  10. Any bets that Greenstrife and its fellow eco-warriors will denounce this as “damaging ti the environment” and a “sidetracking of valuable resources needed for wind technology?”

  11. I’ve actually done some research in the field of carbon-based semi-conductors. Some people are hot & bothered by materials such as nanotubes, graphene, and even rubrene. But so far we haven’t seen the efficiency of these materials.
    Effectively– “you’re doing it wrong”.
    The carbon semi-conductor isn’t the most interesting part– we can make long strands of conjugated pi-systems– an electron superhighway, as it were. But the electrons just don’t jump like the do on a metal semiconductor or on silicon. The efficiency is 3% at most, compared to >30% with alloys of indium.
    IMHO, it’s a pipe dream that any of these materials could match a silicon semiconductor you’d find in a $20 calculator. Carbon pi-systems still have interesting properties, just not the properties people in the semiconductor field are expecting.

  12. LightRain says:
    October 10, 2010 at 10:35 pm
    Carbon is an element of life, unless one is a Carbon Vampire.
    I hear they cast no Carbon Life footprint.

  13. DocattheAutopsy says:
    October 10, 2010 at 11:00 pm
    I guess because we are looking for the CMOS line of solar panels.

  14. How about Solar Paint.
    This story from The New Inventors, ABC TV Australia.
    The invention involves the development of a completely printable organic solar cell based on semiconducting polymer nanoparticles dispersed in water. Essentially these tiny particles in suspension are a water-based paint, which can be printed or coated over large areas. In the first instance these coatings will be put onto plastic sheets that can be placed on the roof of a house. However, in the longer term it will be possible to directly paint a roof or building surface.
    http://www.abc.net.au/tv/newinventors/txt/s3008638.htm

  15. Carbon based energy cells have been around for millions of years. They are called leaves and convert sunlight into energy and push oxygen into the atmosphere.Much better idea.

  16. “DocattheAutopsy says:
    October 10, 2010 at 11:00 pm”
    Indeed, well said.
    “Michael says:
    October 11, 2010 at 1:35 am”
    Yes the carbon infestation at the origin. VEGER, it’s OK, we are the creator!


  17. Even were it possible to collect one hundred percent of the energy reaching the surface of the earth by way of insolation (anybody else instantly flash on Robert A. Heinlein’s 1940 short story “Let There Be Light”?), is it possible for such solar panels to achieve either consistency of output or sufficient power density to make any real contribution to an industrial society?
    The amount of light energy hitting any square meter of the earth’s surface (even at high altitude in relatively cloudless regions) is not all that impressive at a maximum of 950 Watts/m2. This was one of the important considerations when solar power satellites in geosynchronous earth orbit (GEO) were proposed in the 1980s.
    Not only is solar irradiance beyond the atmosphere about half again greater, but in microgravity it is possible to deploy parabolic mirrors of enormous size (aluminized Mylar won’t blow away in vacuum, and micrometeor perforations are unlikely to significantly impair function) to gather and focus such energy. And a powersat in GEO could be made to function 24/7/365 without concerns about planetary rotation, cloud cover, or dusting the vast arrays of solar panels that would be required to make solar power even remotely practicable in places like Barbara Boxer’s Mojave Desert forbidden zone.

  18. Better, cheaper, smaller solar cells are irrelevant to world energy without the storage technology to hold a percentage of the energy from day to night and to cover periods when cloud or snow block the light. Only 17% grid storage is needed yet we see no real efforts to build such infrastructure or price energy in such a way that storage is profitable and is thus privately built. Its been functionally exuded from most carbon trading systems where they have been implemented. Just 15 years ago this was taught to anyone doing renewable energy courses at University, permaculture courses and other places where solar as discussed. Storage technology was developed including underground compressed air storage, battery complexes and solar salt ponds. All have proven profitable where tried commercially. Yet the IPCC an other bodies seem to have gone off the idea finding excuses to ignore the solution. This to me, someone trained in this field, is the strongest proof that the IPCC, Gore and the other advocates of climate change do not want a solution they only want an intractable problem to drive grant engines and political power.

  19. @Perry “Personally, I shall not consume £8,350 of electricity during the rest of my life.
    That’s what you think. If all the taxes that the AGW mob want are fully imposed, that could well be your bill for a month of your current consumption.

  20. As Tarzan would say “carbon not bad, carbon good”. If they can make it work, would it attract lightning. And is oil really a fossil fuel or is it renewable in nature?

  21. Other commenters beat me to the punch. A major problem is energy storage for when the sun isn’t shining.
    That said this would still be wonderful if it can be made practical. Grid interconnects, if the electronics can be standardized and mass produced to achieve economy of scale, eliminate the need for local energy storage. When the sun is shining centralized on-demand power generation can be throttled down considerably and when it it isn’t shining can be throttled up as necessary. Moreover the nature of solar cells lends itself to decentralization of power generation and hence reduces the need to upgrade main high tension transmission lines.
    As with other commenters I tend to agree that the ultimate answer is biological. Nature has been harvesting and storing solar energy for billions of years. We just need to effectively harness the biological machinery that’s already extant in nature. Unlike all the other proposals for alternative energy I’ve seen, synthetic biology is actually progressing at an accelerating rate and should come to fruition (in the famous words of Jerry Pournelle) “real soon now”. It’s difficult to overstress the magnitude of engineering opportunities that become available when the molecular machinery in living cells can be co-opted and customized. Synthetic biology is the next great technological leap and promises to be just as great as anything that came before it.

  22. Peter P. says:
    October 10, 2010 at 9:54 pm
    – The end of eco-fascism
    – Electricity and all its life-enriching benefits
    – Oil and coal and all their life-enriching benefits
    – Cows and all their tasty benefits

    We adhere wholeheartedly!, but the commemoration day should be the 19th November each year, the day when “Climate-Gate” emails were released.

  23. Looks to me as if this is simply more “pie in the sky bye and bye”.
    My personal experience with plastics in general is that they rapidly lose structural strength, particularly when exposed to high temperatures and in particular, UV light, through, as I recall, depolymerization.
    As an old professional civil engineer, I deplore the lack of what was called engineering economics in my day. In all of these schemes, I see no consideration of maintenance and operational costs, no analysis of the period required for return of investment, no amortization of cost over the period of useful life of the physical plant itself.
    Although I am not an electrical engineer, I know from reading that the difficulties of switching an unreliable source of electricity into and out of a power grid to meet demand are huge.
    Lots of smoke and mirrors, the usual “we need more public money for further study”, and the like, is what I see. These “alternative energy” schemes are, from what I have seen, among the least practical, and most expensive by far, ways of producing the electricity we humans need to maintain a reasonable standard of living, let alone the portable power sources we need for individual transportation.
    In addition, the actual cost of fuel is but a small part of the cost of delivering energy to the places where we need the power.
    The way I see it is, while the overall amount of oil, natural gas and coal may be finite, we have in known and exploitable deposits sufficient amounts to provide our power needs for at least 500 years at reasonable cost. I know that there is a process which can, at a competitive cost with crude oil pumped from natural deposits, directly convert any vegetative matter into the equivalent of “light, sweet” crude oil and water. I would expect that further increases in our technology will occur in the next 5 centuries, if we don’t bankrupt ourselves in the meantime, which it looks to me as if we are rapidly doing.
    I fear that more economical and basically non-polluting ways of providing our energy, perhaps more mundane than these hi-tech “scientific” schemes, are being ignored because of the “razzle dazzle” of more hi-tech sales pitches.

  24. We have a big problem here.
    The Green Blogs and MSM are pushing new Green technologies and “world changing inventions” like solar panels, batteries and high performance high range electric cars at an incredible rate making the masses believe that we have all the technology available to create a comfortable life style without oil.
    The problem is that non of these “revolutionary” inventions make it into the market. Those products that make it to the market simply don’t deliver the promised bang to the buck (announced price/performance) and only survive thanks to Government grants, read tax payers money.
    I provide you with an example:
    In 2007 I read about a new revolutionary battery able to power your home allowing you to store wind and solar energy and operate all your existing equipment without restrictions at a price of US 2000 (for a 5 Kw unit, continuous output performance (for several hours).
    The article stated that this battery would be ready for mass production at the beginning of 2008, but when the time arrived, nothing happened.
    In 2009 there was a new head line, same battery, same people, lower continuous output performance but still respectable:
    The header of the articles published all over the world:
    “Revolutionary battery will change the world one home at a time”
    http://www.heraldextra.com/news/article_b0372fd8-3f3c-11de-ac77-001cc4c002e0.html
    They now promised market introduction in 2011.
    I can tell you now that it won’t happen. This battery is nothing more but…. a hoax.
    They probably filled their pockets with development grants (as most of these companies do) and keep developing until they are ready for retirement.
    Similar schemes have been introduced in the car industry that promised us cheap electric cars by 2010 with a range of 400 miles and recharge intervals of 10 minutes.
    This was 1998.
    Because of this propaganda the problem we have today is that poorly informed people simply make the wrong decisions with potentially deadly consequences for our economies.
    I really think this is a dangerous development.
    A few decades ago we never heard anything about the new products that were in the pipeline. These products came on the market and the consumer decided over it’s success.
    Today we have politicians telling us the number of electric cars that will be on the roads in two years and they also tell us the 8 cylinder engine won’t be available for the next generation of cars.
    The market and the consumer are subject to a process of eradication.
    I hope you get my point.

  25. R. de Haan says:
    October 11, 2010 at 10:25 am
    All those funds will disappear as the necessity for equilibrating your economy becomes more evident and with it the urgent need to stop unnecessary expending and a running out of control inflation.

  26. Perry says:
    October 10, 2010 at 10:39 pm
    A much more cost effective scheme to have complete independence would be a Straight Vegetable Oil fueled diesel generator, smart inverter & a few batteries. Leisure boating technology, in fact.
    ——————–
    Now that’s good thinking Perry! With fuel pre-heating you can also use animal fat. The diesel engine has got to be one of the most practical inventions ever (doesn’t even need a spark plug). The inventor – Herr Diesel – ran it on peanut oil, I believe.
    I know, I converted my last van to run on it, because veg oil was 40% of the price of diesel. Then the greenies jumped on the bandwagon, people in developing countries starved more than usual and the price went up. Now it’s only worth doing if you recycle used oil (in the UK).
    And – to stay within the law – I had to register with Her Majesty’s Customs and Excise (as it was then known) as a fuel substitute producer, to allow me to buy veg oil of the supermarket shelf and use it in my van. I had to make a monthly return to them, to account for my usage, so I could pay them the appropriate road-fuel duty.

  27. Anthony, speeking of Halloween coming soon, Do you know where a person can get a CO2 costume to parade around for Halloween??? Just to mock the Warmist/Alarmist!!! HAHAHA!!!
    Or would it would be better to get a Jones or Mann or Gore costume to fit in more with the season of Halloween!!! Or even better a Pachauri costume, HEHEHE!!!

  28. Well the very non scientific public announcement doesn’t say much that gives one any confidence that they actually have a real breakthrough here; and I am not trying to be negative here. I’m always happy to read of new advances.
    But the main thrust of their story seems to be that “excitons” travel a long way in plastic semi-conductors. Well whoop de do !
    One can estimate that about 98% of the TSI lies within the wavelength range of about 0.25 to 4.0 microns, with only 1% remaining at each end of that range.
    So imagine that every single photon with wavelength in that range, is absorbed in their plastic. Let’s even imagine that every such photon absorbed elevates an electron to the conduction band.
    Does that mean that such a device can convert sunlight to electricity at about 98% (energy) efficiency.
    Well I don’t think so. That is a 16:1 photon energy range, and the semi-conductor band gap would have to be low enough to detect that 4.0 micron photon.
    Well a 1.0 micron wavelength photon is about 1.24 electron Volts; energy wise, so 4.0 micron photons would be only 310 millivolts; so their carbon plastic muck would need a bandgap like that; or at least that sort of energy gap for an allowed transition; depending on possible dopant impurities. At the UV end at 0.25 microns, the photon energy is 4.96 eV.
    That 4.96 eV photon is not going to create a shower of 16 electrons and a cell Voltage in the 300 mV range. You are only going to get a single electron per photon; so the rest of that energy simply has to go up in smoke; literally, it will end up as heat (phonons), and not as usable electricity.
    So nyet on the 98% power conversion efficiency.
    A penalty that existing technology “white” LEDs enjoy is that the single diode variety, use a wide bandgap semiconductor usually based on the Gallium Nitride or Indium Gallium Nitride III-V systems to generate a short wavelength light (Blue to UV) and some of those photons are absorbed by a phosphor which emits a broad yellowish spectrum; which when combined with the short wavelength residue, gives some sort of white light.
    The best known such system (patented) is the Ce3+ doped Yttrium Aluminum Garnet; which has a very strong absorption at 460 nm which is a nice blue; and it emits a yellow centered fairly broad spectrum as a phosphor. Put them together properly and a blue in the 460-470 nm range combined with its yellow complement at around 580-585 nm gives the highest lumens per Watt white light possible; soewhere around 400 Lumens per Watt as I recall.
    Well so what; how does that relate to solar conversion. Well many phosphors are known that work better if you use a shorter wavelength; even UV to stimulate their fluorescence; ordinary fluorescent lights use that UV.
    Unfortnately the residual UV doesn’t add to the fluorescence in any useful way; so the extra photon energy over the minimum necessary simply results in an energy loss as heat.
    Well you see, the phosphor is just another form of solar cell; which absorbs photons at ahigh photon energy, creating an exciton or excited electron state; which upon decay results in a lower energy photon being emitted. The remaining photon energy ends up as heat, and not asd more electrons or more longer wavelength emission in the case of the phosphor activated LEDs
    So REAL high efficiency solar cells that have been implemented in practice have been sandwich devices with several (usually three) semiconductor Junctions in series; each with a different bandgap material to efficiently convert a certain range of photon energies to electricity.
    You have to put the short wavelength diode on top of the middel wavelength diode, which is on top of the long wavelength one.
    The highest photon energies are stopped in the top layer which might be a Gallium Nitride junction; and longer wavelength photons will zip right through that into the next layer or the bottom layer.
    Well it is extremely difficult to make heterostructures of totally different crystal species; each of which has a difefren crystal lattice constant; and difefrent coefficient of expansion; so you will get strained lattices which don’t help.
    So there’s a whole lot more to it, than simply havinga material with a long lifetime exciton state; that can travel far enough to get collected by an electrode structure.
    Texas Instruments once made (experimentally) a serpentine silicon junction structure using a highly anisotropic etch and epitaxial regrowth. With the etch they cut channels that were one or two microns wide, and around 200 microns deep; which is totally amazing, creating a nest of silicon blades a micron or two thick, and 200 microns high. And when you put this weird crystal structure into an epi reactor the deposition rate was such that the deeper down the canyou you went; the faster was the deposition rate; in fact it was linear with depth, so the canyons got narrower at the bottom and the walls sloped, until the bottom was a knife edge, and the slope continued to dimiish linearly like that until those original slit canyons were filled in , and the wafer surface was flat again; and they grew a thin top layer over that.
    The epi layer was doped opposite to the substrate, and the end result was a junction diode in silicon, that was folded back and forth over a total thickness of around 200 microns.
    Well that thing would now absorb photons out to a very long wavelegth; that normally would go right through a normal shallow junction; yet the resulting carriers that were geberated; were still within a micron of the junction so they could be collected.
    I don’t know what they did with that technology; but I imagine it wasn’t a cheap process to do. Sure was a spectacular structure though.
    So we shall see what all the Ruckus at Rutgers is if any.
    Now I don’t see any caption of that solar cell array photo, that says that this is one of their new miracle solar cells that “may” be the future of solar energy.
    But I’m sure those chaps would like some more research grant money to bring their idea to “fruition”.
    I’m not too upset by th3e lack of electric storage capability for solar energy.
    R Bucklminster Fuller solved that problem decades ago.
    In the USA, we have a 3 hour time lag from coast to coast; that moves our sunlight with it; and it so happens that our electric usage follows our sunlight cycle as well. Well three hours is still only three hours.
    So Bucky Fuller’s idea was simple. To hell with the East West view of the world. rotate ninety degrees and go north south.
    So now you can have a north over south America connected gridwise over the pole to a Europe and Asia that is 12 hours out of phase with us. So yes with a global power grid; you don’t need storage; but you do need efficient power transmission; and of course political sanity and stability.
    This world is not yet ready for political sanity. But the science is already there in a sense.

  29. You know… I have been following the solar industry for over 2 decades now and every year, 3 to 4 times a year there is an article out about a discovery that will revolutionize solar power and make it worth it.
    Every year…
    Every year…
    yet none of these discoveries ever seems to make it cheaper or really much more efficient.
    Look if payback on a solar cell was one to two years I would do it in a heart beat ( not including government subsidies ) but it isn’t… and seems like it will not be.

  30. I seem to recall that the reason that we use silicon for semiconductors is that it is much easier to grow silicon crystals than carbon (diamond) crystals. Otherwise, I believe, we would expect to see a performance improvement going from semiconductor silicon crystals to diamonds similar to what we achieved going from germanium to silicon.

  31. Spector says:
    October 11, 2010 at 11:22 pm
    I seem to recall that the reason that we use silicon for semiconductors is that it is much easier to grow silicon crystals than carbon (diamond) crystals. Otherwise, I believe, we would expect to see a performance improvement going from semiconductor silicon crystals to diamonds similar to what we achieved going from germanium to silicon. “””
    The change from Germanium to Silicon was mostly driven by operating Temperature considerations. Germanium transistors worked quite well but had very resticted Temperature operating range (high temperature) And the Silicon Planar technology invented by Jean Hoerni at Fairchild Semiconductor, did n’t happen until Germanium was dying out anyway. There are more modern planar Germanium technologies, and even GeSi hetero technologies that can make some damn nice semi-conductor devices.
    But Diamond has too large a band gap to make good solar cells. My Diamond book suggests a conduction band minimum between 5 and 6 Volts above the valence band; and the value from the UV absoption edge is given as 5.4 eV by Clark, Ditchburn & Dyer (1956)
    That would seem to indicate that diamond solar cells would require photon energies beyond the solar UV limit. So nyet on Diamond solar cells. not even as one junction in a multijunction snadwich.

  32. Solar is never going to work its way through the tangle of sporadic input, large equipment costs, and huge placement and infrastructure requirements . Pretending otherwise is either wishful thinking or venal manipulation.
    I have hopes for a kind of Alexander’s Sword chop at the Gordian Energy Knot: there’s a wee research firm’s project which is moving rapidly towards a cusp point in NJ, of all places: check out LPPpower.com or focusfusion.org if you want details. Briefly, it aims for “scientific breakeven” sometime early in the New Year. 2 or 3 yrs. of engineering will, it is hoped, then produce a proven mass-reproducible design for a 5MW generator that will fit in a shipping container, siteable anywhere remote monitoring and twice-yearly servicing are available. Manufacturing licenses to be made available at very reasonable prices to all comers, world-wide. Costs and output at about 1/20 best North American alternatives.
    Solar, wind, and other greenie renewables would/will be immediate economic roadkill. Most conventional plant would follow in due course. And CAGW will die a swift unnatural death.
    Here’s hoping!

  33. P.S. Fuel (boron) estimated to be adequate on-planet at 10X current power demand until about solar red giant time.

  34. George E Smith:
    I sense Nature is pushing materials research on carbon, rubrene and graphene, for whatever reason. Perhaps product placement.
    What about a 3-layer sandwich of graphene on top of rubrene on top of fullerine? Would that absorb anything worthwhile?
    The graphene research might bear greater fruit in semiconductor memory composed of layers of the stuff.

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