From the I’ll believe it when I see it department comes this claim.
From R&D magazine:
Throughout decades of research on solar cells, one formula has been considered an absolute limit to the efficiency of such devices in converting sunlight into electricity: Called the Shockley-Queisser efficiency limit, it posits that the ultimate conversion efficiency can never exceed 34% for a single optimized semiconductor junction.
Now, researchers at Massachusetts Institute of Technology (MIT) have shown that there is a way to blow past that limit as easily as today’s jet fighters zoom through the sound barrier—which was also once seen as an ultimate limit.
They have published a compelling case that the key to greater solar efficiency might be an organic dye called pentacene. More from R&D:
The principle behind the barrier-busting technique has been known theoretically since the 1960s, says Baldo, a professor of electrical engineering at MIT. But it was a somewhat obscure idea that nobody had succeeded in putting into practice. The MIT team was able, for the first time, to perform a successful “proof of principle” of the idea, which is known as singlet exciton fission. (An exciton is the excited state of a molecule after absorbing energy from a photon.)
In a standard photovoltaic (PV) cell, each photon knocks loose exactly one electron inside the PV material. That loose electron then can be harnessed through wires to provide an electrical current.
But in the new technique, each photon can instead knock two electrons loose. This makes the process much more efficient: In a standard cell, any excess energy carried by a photon is wasted as heat, whereas in the new system the extra energy goes into producing two electrons instead of one.
…
While today’s commercial solar panels typically have an efficiency of at most 25%, a silicon solar cell harnessing singlet fission should make it feasible to achieve efficiency of more than 30%, Baldo says—a huge leap in a field typically marked by slow, incremental progress. In solar cell research, he notes, people are striving “for an increase of a tenth of a percent.”
Full story here
The paper:
External Quantum Efficiency Above 100% in a Singlet-Exciton-Fission–Based Organic Photovoltaic Cell
Daniel N. Congreve*, Jiye Lee*, Nicholas J. Thompson*, Eric Hontz, Shane R. Yost, Philip D. Reusswig, Matthias E. Bahlke, Sebastian Reineke, Troy Van Voorhis, Marc A. Baldo†
Science 19 April 2013: Vol. 340 no. 6130 pp. 334-337 DOI: 10.1126/science.1232994
Abstract
Singlet exciton fission transforms a molecular singlet excited state into two triplet states, each with half the energy of the original singlet. In solar cells, it could potentially double the photocurrent from high-energy photons. We demonstrate organic solar cells that exploit singlet exciton fission in pentacene to generate more than one electron per incident photon in a portion of the visible spectrum. Using a fullerene acceptor, a poly(3-hexylthiophene) exciton confinement layer, and a conventional optical trapping scheme, we show a peak external quantum efficiency of (109 ± 1)% at wavelength λ = 670 nanometers for a 15-nanometer-thick pentacene film. The corresponding internal quantum efficiency is (160 ± 10)%. Analysis of the magnetic field effect on photocurrent suggests that the triplet yield approaches 200% for pentacene films thicker than 5 nanometers.
Some figures:
Figure 1 Singlet fission dynamics in pentacene.
Calculations of singlet and triplet excitons and charge transfer states at the pentacene/fullerene interface are shown, with the purple (orange) density indicating where less (more) electron density is found in the excited state. The delocalized singlet exciton and two localized triplet excitons are circled in red. The loss pathway for singlet excitons is direct dissociation into charge before singlet exciton fission.
Fig. 2 Device architecture and EQE of a pentacene solar cell.
(A) Chemical structures and architecture of the solar cell with the thickness of each layer in nanometers and energy levels of the lowest unoccupied and highest occupied molecular orbitals in electron volts (12, 18, 20, 29–31). The anode is composed of indium tin oxide (ITO) and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). The cathode employs bathocuproine (BCP) and a silver cap. (B) External quantum efficiency of devices without optical trapping (blue line), and device measured with light incident at 10° from normal with an external mirror reflecting the residual pump light (red line). Optical fits from IQE modeling are shown with dashed lines: modeled pentacene EQE (blue dashes), modeled P3HT EQE (purple dashes), and modeled device EQE (black dashes) for comparison to the measured device efficiency without optical trapping.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
The greens will not like this…
The headline makes no sense. That’s not the claim the paper is making. The paper is claiming that energy that otherwise would have gone into heat, is instead put into moving two electrons instead of one. If it work exactly as claimed, then the efficiency would still be well below 100%.
REPLY: Look at the figure 2 graph, over 100% (I’ve updated the headline and added a section from the R&D article to make the distinction of quantum efficiency and overall efficiency clearer) – Anthony
Over 100% efficiency? Wonderful!
Use the first 100% of to power a light above the cell to generate yet more electricity and use the rest for something else.
Once you have it started, you’ve got an endless supply of free energy. .
What could possibly be wrong with that idea.
Judging by the context,what they mean by “quantum efficiency” isn’t the ratio of electric energy out to photon energy in but the ratio of electrons out to photons in.
There is always hype in research and as you say we will just have to wait and see. Just in case there is some confusion, I will point out that quantum efficiency is a much different thing then thermodynamic efficiency. This is made clear in the linked article where it is also stated that the thermodynamic (overall) efficiency is only 2% in the device at present. Quantum efficiencies greater than one (100%) are not unusual. What the authors claim is new is the extension of this from the ultraviolet into the visible. They may, of course, be underestimating the problems yet to be surmounted, but such is the game of research.
“Singlet exciton fission transforms a molecular singlet excited state into two triplet states, each with half the energy of the original singlet”…. Not sure of the physics in this, but it sounds like all they’re saying is that this process yields more electrons at the same (or closer to the) total energy of the photon, whereas the previous process only could yield a single electron at a certain energy level, with excess energy from the photon being lost as heat. The above sounds like there’s no claim of violation of the 2nd law (e.g. more energy out than in). Also, doesn’t a high energy gamma (nothing more than a very energetic photon) produce thousands of free / knocked loose electrons as part of the ionization process? Each one takes some of the energy from the gamma…..no violation of 2nd law there even though it frees up thousands of electrons per photon. Of course, I do agree with the sentiment of show me. And detail how you did it so it can be independently replicated (e.g. real science), don’t pull the whole “peer review” pseudo-science.
OK we’re talking about converting Radiant Energy (Photons) to Electrical Energy (Electrons). So how many Photons = 1 Electron, or is it as I suspect more complicated than that?
William Sears:
You beat me – and I suspect several others – to it.
Well done!
Richard
Sorry, but your headline is completely misleading. 100% efficiency for a solar cell would mean that all of the incoming solar radiation is converted to electricity. That is not what the article claims. The science may or may not be legitimate, but your headline is 100% wrong.
The writers talk of taking PV panel efficiency from 25% to 30%, not a bad improvement.
I do not know where the 100% cam from.
REPLY: it is in the title of their paper:
External Quantum Efficiency Above 100% in a Singlet-Exciton-Fission–Based Organic Photovoltaic Cell
– Anthony
This reopens a ‘discussion’ into Einstein’s view on light propagation and photons. Also the differences between emitted and absorbed photons.
100% efficiency would be 1 watt out for every watt in. In theory there should be nothing to stop one sufficiently energetic photon from knocking loose many electrons, if the electrons are sufficiently loosely bound. Of course, in practice …
Is what this is really doing is [potentially] boosting the Shockley-Queisser efficiency limit to 68% at certain wavelengths? This effect would be wavelength dependent? Am I understanding correctly that 670nm seems to be a critical wavelength and less energetic photons won’t have enough energy to eject two photons? Thus what would the real efficiency gain be assuming normal sunlight? Of course if you are also reducing thermal gain to the cell you might reduce loss of efficiency to increasing cell temperature as well.
It will be interesting to see what comes of this. Potentially a game changer.
OK, I see that your headline has been updated. Disregard my previous comment.
REPLY: yes there’s a difference between overall efficiency and quantum efficiency, and it is important to make that clear – Anthony
Brilliant! Pentacene + Dilithium Crystal – Add a mirror backing and a one way mirror, atop, and start it with a laser…
“Look out, Jim.. she’s gonna blow!”
Or is it really an ambient temp superconductor…
“The Power Companies hates this simple trick! Click here!”
“Well hell yeah, why not.. I was playing pool last night and pocketed 2 balls on break, twice, and 3 one time”
It’s April 28, fucrineouloud.
I keep seeing confusion about the First and Second Laws of Thermodynamics….
Converting local heat into electricity is a Second Law violation. It does not imply a First Law violation. It doesn’t mean you can use a unit to power itself and produce even more energy. That would be a First Law violation, and something completely different.
At most, this line leads to a situation where the conversion of phonons into electron/hole pairs is statistically more probable than the reverse. That isn’t anything like trying to convert previously non-existent energy into electron/hole pairs.
If the cell was 100% efficient you would not be able to see it since all the light striking it would be converted to electricity.
Longevity may be an issue here, pentacene is sensitive to moisture and oxygen at the molecular level, The resulting solar panel will have to be perfectly sealed.
The solar panels on my roof are reckoned to last about twenty five years before the output starts to drop off significantly. Just guessing, but if each photon starts knocking off twice as many electrons, doesn’t that imply that the panels will last half as long?
No, the electrons are circulated through the materlal and the external circuit. You don’t “run out of” electrons.
If the cells were 100% efficient you wouldn’t be able to see them since all the light striking them would be converted to electricity.
Typical thin film efficiencies aren’t much beyond 10%. Crystalline are around 16 to 18% as
I recall. Whether the greater efficiency is valuable depends on the added cost to achieve same.
My calculations show 80,000 acres of thin film commercial panels needed to produce the same amount of power as a modern nuclear reactor plant, although the power is uncontrollable and is
thus not worth anywhere near as much. If they manage to double efficiency of thin film commercial panels, then “only” 40,000 acres would be needed to match the bulk output of a nuclear
plant. Whoopee.
Reminds me of the math used to calculate GDP in Q1 2013.
They managed to show growth of 2.5% rather then a loss of .5%
😉
Yea I would be careful about this one. It looks like the quantum efficiency is increased not so much by this effect but by the mirroring of the light. Also, there is a huge gap between what looks good in the lab and what works in the manufacturing environment.
In the typical photovoltaic cell, a cubic crystalline Silicon base, with four outer shell electrons, is irradiated with Boron having five and Phosphorus having three outer shell electrons. Sunlight ‘excites’ the one, least stable, outer shell electron, which ‘flows’ thru the Phosphorus electron ‘hole’, exiting the cell as one-way, direct current. This is molecular erosion that never returns the mining, refining, manufacturing, transporting, installing and in less than 20 years, disposing of this solar Ouija board parlor trick. Forcing an extra electron out of one of these three grid materials would make only a marginal difference in this electron erosion process. More on this in, “The Green Prince of Darkness”….
One Wonders Where the World Would Be….Without these Wicked Weather Wiccans….
or the banking Ponzi scheme that has finally gotten so bad, even the greennies have noticed….
http://www.rollingstone.com/politics/news/everything-is-rigged-the-biggest-finacial-scandal-yet-20130425
[the green meanie thingy is rigged]