Clean Power

Published on July 11th, 2014 | by Sandy Dechert


Solar Cell Efficiency Rises By 30% Through Singlet Fission

July 11th, 2014 by  

Scientists were pretty excited when they discovered you could convert light energy directly into electricity by capturing photons in semiconductors, exciting them into “excitons” (bound electron with negative charge and hole with positive), and capturing the resultant current through electrodes. Now a group of four chemists from the University of California, Riverside, has worked out a way for one photon to generate a pair of excited states rather than just one.

Christopher Bardeen, chemistry prof at UC Riverside, speaks at Northwestern's ANSER Solar Energy Symposium ( Christopher Bardeen, chemistry prof at UC Riverside and singlet fission pioneer, speaks at Northwestern’s ANSER Solar Energy Symposium ( 

It’s called “singlet fission,” and by using it, we should be able to boost solar cell efficiency by as much as 30%, providing “Third Generation” solar power. The Journal of Physical Chemistry Letters published the research results in an Editor’s Choice perspective article last month.

Christopher Bardeen, the chemistry professor whose lab led the research, explains what sent him  along this line of inquiry:

Our research got its launch about ten years ago when we started thinking about solar energy and what new types of photophysics this might require. Global warming concerns and energy security have made solar energy conversion an important subject from society’s point of view. More efficient solar cells would lead to wider use of this clean energy source.

“If a triplet exciton has half the energy of a singlet, then it is possible for one singlet exciton, generated by one photon, to split into two triplet excitons,” Dr. Bardeen explains. “Thus, you could have a 200% yield of excitons—and hopefully, electrons—per absorbed photon.”

Here’s the Bardeen lab’s diagram of how singlet fission works to spontaneously split into two triplets, effectively dodging the efficiency barrier of the Shockley-Queisser limit.

Singlet fission adds to PV potential (Bardeen Lab, UC Riverside)
“The exact mechanism is unknown, but it does happen quickly—at the sub-nanosecond timescale—and with high efficiency,” Bardeen says. His lab’s work has shown that it is very sensitive to molecular alignment and position.

Bardeen cites recent work at MIT that has already demonstrated an organic photovoltaic cell with more than 100% external quantum efficiency based on this effect. Bardeen believes we can use this effect to raise the efficiency of inorganic semiconductors.

Next steps: finding new materials that exhibit singlet fission, figuring out how to turn the triplet excitons into photocurrent efficiently, and determine how the spin properties of the electrons affect exciton dynamics.

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About the Author

covers environmental, health, renewable and conventional energy, and climate change news. She's currently on the climate beat for Important Media, having attended last year's COP20 in Lima Peru. Sandy has also worked for groundbreaking environmental consultants and a Fortune 100 health care firm. She writes for several weblogs and attributes her modest success to an "indelible habit of poking around to satisfy my own curiosity."

  • jackgotney

    Nanoflex Power Corp just received a patent for something along these lines (through research sponsored at U. of S. CA (USC)). It was applied for in 2008 under scientist ME Thompson and I understand they demonstrated experimental results but I don’t know what they were 9,391,284 :
    Organic photosensitive optoelectronic devices with triplet harvesting
    There is disclosed an organic photosensitive optoelectronic devices comprising organic photoconductive materials, which comprise singlet fission host materials doped with triplet forming materials. There is also disclosed devices made from such materials, such as an organic photovoltaic cell, a photoconductor cell, a photodetector, organic photosensors, chemical sensors, and biological sensors.
    Methods of fabricating such devices are also disclosed.

    Even though they funded a ton of research in the organic solar field, I think their biggest breakthrough has been in the (inorganic) GaAs thin film area where they developed a process for manufacturing very efficient (25% or more PCE) light weight low cost flexible long lived thin film GaAs Solar panels at less than 3% percent of the current cost. They found a way to grow them from GaAs wafers and reuse the wafers without destroying them, unlimited times. They have successfully developed ways to drastically speed up the epitaxial liftoff process. This will probably emerge to compete with specialty and then mainstream solar before Organic Solar really takes off. But organic solar will have its day. It is not that far away. Once these chemical / electrical engineers have figured everything out they will probably be able to produce thin film organic so cheap it fill a large market depsite its being shorter lived and also not as efficient as the Inorganic and inorganic hybrid counterparts just because of the low cost, non-toxic, plus portable factor.

  • luke

    the business case is the key here. the absence of immediate adoption potential by industry of the idea seems to significantly undercut the utility of it

  • Hans

    Only the image to the article reveals that the research concerns organic solar cells. Organic solars have the potential to be produced cheaply but currently have a low efficiency (about 8% for single junction). With an efficiency improvement of 30% it would reach an efficiency of 10.4%, still much less as conventional silicon solar cells.

    The title and the article are therefore somewhat of an overstatement.


    Don’t know why this of all things is getting so hyped up by the blogosphere. Nothing new was demonstrated, invented or discovered. It is an analysis of a known effect that so far has not been very effectively implemented. It also applies only to organic solar cells which have a record lab efficiency of about 12% and so won’t have impact on the solar industry for some time. Not that it isn’t interesting, but why is it so hard to just report on the facts without hyping it up and making the field look bad when it doesn’t live up to ridiculous headline claims?

    • IMPOed

      Any and Every advancement should be applauded, no matter how “tiny”, we are living in the trash bin of the fossil fuel industry and I for one am sick of it!
      I am interested in anything this field produces that will instill hope for the future, your arrogance in assuming that just because you “know-it-all” we all should attitude, is not advancing anything but the world worn statuesque, why bother, well I “bother”.
      BTW, up-voting yourself doesn’t add to your credibility.

      • UM_GSRA

        I bother by working in the field and understanding the science. And yes everyone should know facts not headline hype. Science doesn’t progress by applauding, only by demonstrated merit something that would serve our society well.

        By the way where exactly do you think organic semiconductors come from? I’ll give you a hint: has a lot more to do with dinosaurs than Michelle Obama’s garden.

        • IMPOed

          You didn’t understand a word I said, why did you even bother to reply?

          • UM_GSRA

            I guess your armchair politics and science philosophy is just too deep for me. But by all means keep dismissing criticism of people who know better in favor of blind hype. You say you want to know anything that instills hope, but without selecting things and publicizing them proportionally to their merit it’s just all noise. That helps no one…

          • IMPOed

            Sorry I bothered you,,,

    • Bob_Wallace

      “BTW, up-voting yourself doesn’t add to your credibility.”

      It’s just plain tacky….

  • jburt56

    My guess is within 10 years.

  • Adam Devereaux

    Very theoretical as James says, I agree that stories like this need to be treated with the right tone. However the sci-fi geek in me loves this:

    “Next steps: finding new materials that exhibit singlet fission, figuring
    out how to turn the triplet excitons into photocurrent efficiently, and
    determine how the spin properties of the electrons affect exciton

    This honestly sounds like Star Trek technobabble. But to me this one paragraph shows why our future is very different from our past. Why Solar and other renewable technologies have legs. We have the ability to understand our world and the underlying physics around us in a way far beyond anything in our recent past. It’s not one discovery, its the magnitude of little steps of progress in every field multiplying to produce unimaginable tools and capabilities to change our world.

    The current lifestyle and struggle of the vast majority of humans on this world IMO is due solely to the selfish, ignorant and arguably xenophobic protectionist mindsets of the masters of government and industry. Trying to protect a way of existence for man and country that led to success and power in the past. An approach no longer required based on the knowledge and capabilities we now have as a species. Look at all the damage our government in the US has caused to the middle east and other countries by playing god with despots and governments.

    I’m starting to sound like the conspiracy theorists that I normally deride. But as I age I wonder if we can ever shed the shackles of tradition to the point that we can truly do better for this world. It’s like the old saying that medicine changes when old doctors die. Its no conspiracy to state that after the 70’s there was a concerted effort by the fossil fuel industry to put the breaks on government efforts towards renewable energy and that effort set us back decades as a country and caused likely trillions of dollars of damage to our environment that we all depend on. So much for understanding the common good.

    Good luck humanity- we are going to need it.

    • Bob_Wallace

      “We have the ability to understand our world and the underlying physics around us in a way far beyond anything in our recent past.”

      Excellent point. We are so far past the stage at which science was “Let’s mix this and this together and see what happens”. We now understand things at the atomic levels and can do much of our experimenting with computer models.

      ” But as I age I wonder if we can ever shed the shackles of tradition to the point that we can truly do better for this world.”

      As someone who has done a bit of aging, I can assure you that we have cast aside a lot of the shackles of tradition. Others will fall as time goes along, I can see that by looking at the young adults who are 50 years younger than me.

      Our real problem, and one which might always be with us, is that some of us are simply more greedy and/or power hungry than most of the rest of us. I expect we’ll have to continuously fight back those who try to grab more than a fair share.

  • saurdigger

    Please change the heading to “could change”. Potentiality doesn’t mean actuality and it’s misleading.

    The image used and quotes used by writers from the researchers are more realistic.

    • Poechewe

      Some caution is helpful. But there has been an explosion of ideas in wind, solar and energy storage in the last decade. And as we can see with the rapidly falling prices of solar and wind, these things are panning out. Even storage systems are beginning to fall in cost.

      If even five percent of these discoveries and ideas continue to pan out, we’ll be in good shape — IF we let these things flourish.

      • saurdigger

        Not trying to be a downer, but I’d rather see “potential to increase efficiency by 5-10% in real life panels” with would be incredible and more realistic, than overhyping something.

        I think it’s a cool discovery. Incremental change can increase those exponential slope angles. 🙂

  • JamesWimberley

    This is very much at the theoretical frontier. There aren’t even lab devices yet, let alone commercially feasible ones. What we can draw from such discoveries is a reasonable hope that the solar learning curve will continue beyond 2020. It won’t stop at 50c per watt.

    • Maventwo

      Another progress of silicon based photovoltaic is to make the surface darker so it will absorb rays from the infrared wavelength spectrum as todays photovoltaic’s can’t absorb rays from.
      Both photovoltaic’s and cam sensors of today have the same problem that they can’t absorb rays from the infrared wavelength spectrum.
      Harvard spin-off company SiOnyx have developed one tech for making the silicon surface darker for cam sensors so they can absorb infrared wavelength rays so cam sensors can see in darkness, good for surviliance cams.
      Danish start-up company Blacksiliconsolar have developed another tech for making the surface of silicon wafers darker so photovoltaic’s will be better in it’s energy absorbation.
      Especially at dawn where todays photovoltaic’s can’t absorb any energy from sun rays.

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