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.
If true sweet 🙂
One question: Does “External Quantum Efficiency Above 100% in a Singlet-Exciton-Fission–Based Organic Photovoltaic Cell”
Really mean: We are well over the 34% limit?
Even that would be amazing. Extra ordinary claims require extra ordinary proof. I’ll wait on this one for further validation and clarification of terms.
Well played sir! And you know the sad thing is that there is probably an actual majority that believe in that exact scenario. They’re easy to spot because they are the ones scratching their heads trying to make a car run solely off the alternator 🙂 Needless to say they’re also the ones that gravitate to AGW and other pop-Science.
Also well played!
Q. Daniels
Looking beyond just sunlight on solar cells, what if we had near 100% conversion of monochromatic photons to electrons coupled with a quantum refrigerator, might we be able to cool with photons?
However, if we have a rectenna with a quantum refrigerator lit by polychromatic light with 70% conversion efficiency via a rectenna, then it wouldn’t that depend on whether the quantum refrigerator efficiency could accommodate the 30% solar to heat conversion?
I don’t know if anyone has added, what they did was redefine the old efficiency limit as 100% and then noted they’ve made a new process with a greater efficiency of photon –> electron transition which, relative to the old theoretical limit, is “over 100%.” It’s a quirk expressing efficiency as a derivative percentage of a more traditional definition of efficiency.
Just make sure that half the flywheels spin clockwise and half anti-clockwise, no problem then.
Well the paper as described is a bit misleading, but not necessarily a falsehood. I didn’t read anything about the cell Voltage that you get with this process.
A normal common garden variety silicon junction, puts out a cell Voltage of about 0.50 Volts, at maximum power loading. At lower loading (higher load tresistance), the cell Voltage increases up to the open circuit Voltage, which is in the 0.6 -0.9 Volt range, and depends on the material bandgap. At heavier loads, (lower resistance) the current increases up to the short circuit current, but the Voltage goes to zero.
The short circuit current is proportional (roughly) to the cell irradiance (W/m^2), while the OC Voltage is proportional (roughly) to the log of the irradiance.
For photon energies below the bandgap, the material is essentially transparent, so the radiation photon passes through the cell, and doesn’t get absorbed. photons above the bandgap energy, do get absorbed. That’s the PV effect Einstein got his Nobel for. The higher the photon energy above the bandgap, the shorter is the absorption length, so the electron is released closer to the surface. I has to make it across the junction to end up as external current, so at some point higher energy photon efficiency suffers from loss of the carriers. So-called “blue” cells, use thinner layers to ensure efficient capture of the electrons, but at a loss of lower energy photons that go right on through the thinner cell, without getting absorbed.
As the paper points out, photon energy above the bandgap generally results in heat losses.
You may get two electrons emitted, in these materials, but what is the cell Voltage at maximum power load.
Incidently, photo-multiplier tubes, rely on multiple electron emission, not so much from input photon energy, but from electron multiplication due to the acceleration of the emtted electrons in between dynodes. Some materials used in PM tubes, notably the III-Vs GaAs, and GaP can emit a half dozen or more new photo-electrons.
The problem of higher energy photons is the reason for multi junction multi bandgap solar cells. The blue bandgap layer is on top, and stops the highest energy photons. The red layer stops the next longer wavelength photons, which go right through the blue layer, and the bottom layer is GaAs or something similar, which can capture the near IR photons, that go through both the upper layers. Present record for a triple junction triple bandgap solar cell is about 43.5 % conversion from solar W/m^2 to DC power out. Dunno offhand what the optimum load cell Voltage is, but it is for three bandgaps in series.
This new cell adresses the energy lost above the bandgap as heat.
Incidently the 670 nm photons they mention are about 2.0 eV energywise So what do you get if you have 1.9 eV photons, or 1.8 e V photons, in the way of cell Voltage that is. Do you always get two electrons of the same energy, or one higher and one lower ?
The important thing is what is the response of this cell to a full solar spectrum of say air mass 1.5 spectral composition ( ground level sunlight)
“””””……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.”……….”””””””””
Note that “should make it feasible ”
Nowhere does it say they demonstrated a solar cell with more than 25% efficiency let alone 30 %
“A solar cell’s quantum efficiency value indicates the amount of current that the cell will produce when irradiated by photons of a particular wavelength. If the cell’s quantum efficiency is integrated over the whole solar electromagnetic spectrum, one can evaluate the amount of current that the cell will produce when exposed to sunlight. The ratio between this energy-production value and the highest possible energy-production value for the cell (i.e., if the QE were 100% over the whole spectrum) gives the cell’s overall energy conversion efficiency value. Note that in the event of multiple exciton generation (MEG), quantum efficiencies of greater than 100% may be achieved since the incident photons have more than twice the band gap energy and can create two or more electron-hole pairs per incident photon”
http://en.wikipedia.org/wiki/Quantum_efficiency
Choey Tuqiri says:
April 28, 2013 at 10:47 am
“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.”
Not if using photon entanglement imaging, experiments has shown that “normal light” have statistically enough “entangled like” photon to generate usefull imaging.
Lockheed has already patented a quantum radar based on this principle. They made progress indeed…
Also a perfect blackbody is not invisible by itself if the background is not black.
“””””…..John says:
April 28, 2013 at 9:40 pm
“A solar cell’s quantum efficiency value indicates the amount of current that the cell will produce when irradiated by photons of a particular wavelength……”””””
Quantum efficiency is simply electrons per photon, in the case of solar cells, or verse vicea in the case of LEDs. Nothing more, nothing less. In the case of a solar cell, that would be electrons kicked from the valence band into the conduction band, for INTERNAL quantum efficiency. If the electron makes it across the junction, without getting reabsorbed, it will likely make it to the terminal, and contribute to the external circuit current. At that point the ratio of electrons to input photons is the EXTERNAL quantum efficiency. QE is not the same thing as conversion efficiency, which is electric otput power Volts x Amps versus radiant power in (Watts).
Materials which make good LEDs, are also good solar cells. If light generated inside an LED gets trapped optically inside the chip, which is typically a high refractive ndex material, the photons will eventually be reabsorbed by the diode, and generate a current opposite the externally applied current. The best LED structures have very close to 100% internal quantum efficiency, and their overall efficiency is limited by optical (TIR) trapping. A new InGaN LED grown on a native GaN substrate, and sawn into equi-triangular die, developed by Sorah (Shuji Nakamura) has very high external QE as a result of high internal QE and efficient optical extraction.
Shockley-Queisser efficiency limit, it posits that the ultimate conversion efficiency can never exceed 34% for a single optimized semiconductor junction.
jet fighters zoom through the sound barrier—which was also once seen as an ultimate limit.
But hang on, are you telling me there are sceptics out there who didn’t believe the science?
Over 100% efficiency is impossible. 2nd law takes over.
Excellent work.
More than 100% effciency is the quantum efficiency: single photon frees more than one electron.
Energy efficiency is still well below 100% – of course!
Efficiency aside, you can’t get past the simple fact that the energy in a square meter of sunlight is pitifully diffuse compared to fossil/nuclear fuels.
Maybe the next “breakthrough” will be solar-cell-lined windmill blades….
I did graduate research in the early 90’s in fullerenes. At the time, they were a chemical marvel and were going to “change the world”. After 5 years and untold money, we were not able to produce one useful, viable application for them. I am happy to see they may be commercially useful somewhere.
More “energy produced” than energy “received”? As I read it, does not seem possible with current technology IMO.
Increasing the efficiency of solar cells is all very well and good but, even if efficiency was 100% there are still major flaws with solar technology and the implementation of it.
The future of solar cells should be concentrating on the “smart devices market” such as all these souped up web enabled smart phones and touch pad devices, the reason behind this is, more and more people will not be buying laptops, PC’s and Mac’s in the future as smart devices suit the majority of peoples needs, even laptops have only a short battery life which makes them less portable, if company’s concentrated on supplying a solar charger with every new smart device then this would remove these devices from the electrical grid.
Instead of creating an expensive solar energy disaster, that solar companies pushing their product to take over an electrical grid with inferior technology from the top down would, they should evolve the way every other technology does, from the bottom up and begin to take advantage of vast markets suitable for the product they have.
Many people writing comments are confused by what Quantum Efficiency means and do not understand how it can be above 100%.
Please read the Wikipedia intro to Quantum Efficiency:
“The quantum efficiency (QE), or incident photon to converted electron (IPCE) ratio,[1] of a photosensitive device or a charge-coupled device (CCD) is the percentage of photons hitting the device’s photoreactive surface that produce charge carriers….”
“…Note that in the event of multiple exciton generation (MEG), quantum efficiencies of greater than 100% may be achieved since the incident photons have more than twice the band gap energy and can create two or more electron-hole pairs per incident photon.”
“”””””…..johnmarshall says:
April 29, 2013 at 2:37 am
Over 100% efficiency is impossible. 2nd law takes over……”””””
Well don’t keep us all in suspense. Just what is it the secomd law has to do with quantum efficiency.
We are waiting on you to enlighten us.
How about you consider this. Light photon triggers a response in any medium. The most efficient responder delivers or excites a measured result. Question; is silicon a generator of electrons? Is the silicon (heat) excited and therefore a generator of electrons. What material could generate or be excited more intensely per unit of light converted to heat? Or would it be better to use fiber optic (glass tubes) to switch triggers and generate an electricity field or electro magnetic response?
Seems to me solar using sili_con is a bad joke played on action response mechanisms.
>100% *quantum* efficiency is still only about 30% *energy* efficiency.
All that is going on here is a novel mechanism that allows collecting more energy from the incoming photon. Note that this is wavelength dependent – photons with wavelengths too long (i.e. low energies) will not excite the singlet state at all. Photons with too much energy will only lead to more thermal energy in the matrix and the emitted electrons – energy efficiency drops off.
“””””…..massagrabber (@MASSAGRABBER) says:
April 30, 2013 at 8:39 am
How about you consider this. Light photon triggers a response in any medium. The most efficient responder delivers or excites a measured result. Question; is silicon a generator of electrons? Is the silicon (heat) excited and therefore a generator of electrons. What material could generate or be excited more intensely per unit of light converted to heat? Or would it be better to use fiber optic (glass tubes) to switch triggers and generate an electricity field or electro magnetic response?
Seems to me solar using sili_con is a bad joke played on action response mechanisms……”””””
Well massagrabber, I think you meant to post this on the Martha Stewart dishwasing blog.
The mechanism cited in this paper has been known (of) for quite some time. The paper cites observation of it under specific conditions in a specific material (pentacene). It does not describe the conversion of the complete earth surface level solar spectrum energy to electricity; and it makes no assertions relating to energy conversion efficiency of any device, and does not involve any thermodynamic considerations.
But it is a long way from a means to getting efficient solar energy conversion.
As it happens, there is a solar energy; mostly PV symposium, tomorrow at UC Davis. If I can find anyone who is in on this pentacene two electron gig, and learn anything, I’ll post something.
Well I said I would ask about the process described in this paper, at the UC Merced Solar Symposium, held at UC Davis today.
The very first paper was a very informative about the history of solar cells in the USA. The first actual application of solar cells in the USA was actually a project most of you are too young to know about, let alone remember.
In 1958, too late to get in on the big international geophysical year gig, project Vanguard, which had degenerated to project rearguard, finally succeeded in launching Vanguard 4 carrying a satellite about eight to ten inches in diameter. Vanguards one through three had gloriously blown up on launch destroying the satellites. #4 finally made it, a year after Sputnik. Built for the Navy, V-4 was battery powered, for reliability, but it had on its surface, about six solar cells about one inch square each. The builders wanted nothing to do with these unreliable solar cells (silicon), so they were separate, and could only be switched on, once the reliable battery power ran out.
So V-4 beeped annoyingly for a few days, while the batteries lasted, on a 40 MHz frequency band.
Then the solar cell crap, bult by Hoffman electronics; most of you have never heard of, at about $150 a piece, got turned on. V-4 then became a total nuisance, as those unreliable Hoffman solar cells powered V-4 for the next 7 years. Nobody built in an off switch, so that band was dead, until V-4 finally did the graveyard spiral thing.
So this speaker actually had with him, the actual Vanguard 5 satellite, that never did get launched. He did admit that the six antenna rods were replacements, the originals having been damaged down through the years. I guess the Smithsonian don’t realize that this chap still has their gizmo.
He incidently is with NREL, the National Renewable Energy Laboratory in Colorado.
I asked him about the two electron process, which he is aware of, but he said it only works at specific photon energy input. So it simply doesn’t operate at all wavelengths with a solar spectrum input.
So not a fraud, but not any panacea, and just one more process that dodges one bullet, only to run into all the rest. Maximum solar cell conversion efficiency is still 44%, about same as at last year’s symposium in Merced.
Deliberately not dropping hisname, since I didn’t make written notes of our conversation.
Symposium was very informative, and better than last year. But the general tone was set by all these folks swilling at the public trough, and complaining that their biggest problem was not price competition from communist red China, but price competition from a plentiful energy source known as natural gas; now called “frack” gas.
So they are all promoters of CA prop 32, which outlaws fossil fuels.
The science papers were very good however. Some very practical; some science interesting, but going nowhere. This chap also had a Solyndra solar tube, which was exactly the size of a four foot T-8 fluorescent tube. He said NREL had measured this contraption at 21% conversion efficiency; but not in a rooftop installation.