"Shadow state" discovery could dramatically boost solar power efficiency


December 22, 2011

Extra electrons harvested from a photon's quantum "shadow state" could boost the efficiency of solar power (Photo: Shutterstock)

Extra electrons harvested from a photon's quantum "shadow state" could boost the efficiency of solar power (Photo: Shutterstock)

Researchers at the University of Texas say it is possible to hike the energy yield of solar cells by exploiting what they call a photon's "shadow state", doubling the number of electrons that may be harvested in the process. They claim the discovery could up the theoretical maximum efficiency of silicon solar cells from 31 to 44 percent.

Prior research led by chemist Xiaoyang Zhu demonstrated that a theoretical increase in efficiency to as high as 66 percent would be possible if solar cells could be made to additionally harvest so-called "hot electrons", residual heat energy that is lost within about a picosecond after a cell absorbs a photon. Zhu then found that this was possible, but only when harvesting photons from "highly focused" sunlight, impractical in real-world applications.

But the team's latest findings point to an alternative means of boosting efficiency. The organic plastic semiconductor pentacene, when absorbing a photon, creates an exciton (an electron paired with an electron hole) which is quantum mechanically coupled to a dark "shadow state" multiexciton from which an additional electron can be harvested. This way, a photon provides double the electrons. Zhu says that the process could see solar cell efficiency increase to 44 percent without the need for a focused solar beam.

"Plastic semiconductor solar cell production has great advantages, one of which is low cost," said Zhu. "Combined with the vast capabilities for molecular design and synthesis, our discovery opens the door to an exciting new approach for solar energy conversion, leading to much higher efficiencies."

The latest University of Texas findings were published on December 16 in Science.

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James Holloway James lives in East London where he punctuates endless tea drinking with freelance writing and meteorological angst. Unlocking Every Extend Extra Extreme’s “Master of Extreme” achievement was the fourth proudest moment of his life. All articles by James Holloway

With the greatest respect to Dr. Zhu and the U of T, plastics will also have to improve in several ways in order to create a real-world cost advantage over the recently-inexpensive mono-crystaline PV panel; which will output power for 20 to 30 years before solar-cell degradation might make it worthwhile to replace.

If the good doctor can demonstrate a panel (a system of components and their electrical junctions) that offers both lower cost and higher efficiency while also enduring blistering sun and/or harsh winters for a minimum of 20 years, I\'m sure he will have a stampede of demand.


While this would be great news if it can be implemented on a commercial scale, It seems that the PV industry is hit with \"New, Improved\" (sans \"bold new graphics\") biannually. Why would any corporate entity or homeowner, for that matter, commit to the huge capital expenditure when a huge improvement is rumored to be available \"soon\"? With \"soon\" to be expected just after the final check clears, prudence would dictate a \"hold\" status be applied to such plans.


It is exciting to hear about the progress and it is also exciting to see new affordable products coming to market now. I agree with Burnerjack. This field is constantly making leaps in capacity. People don\'t want to put something expensive on their roof that is going to be obsolete or outmoded in a season. Maybe if these companies committed to a platform that would accept recycling of less efficient panels to swap them out for the newest and best panels that could give the consumer some peace of mind. This type of swap-able panel system would justify the cost of investing in the technology of today for the promise of access to the best tomorrow.

Carlos Grados

Any news about increased PV efficiency is good news. I look forward to the day when this technology is available, as I\'m sure many, many other people do as well. Some of the thin-film modules are very, very close to grid parody. This technology will make PV even cheaper, and make it lower priced than carbon based energy.

Carbon based energy is on an upward trajectory cost wise, while PV is on a downward trajectory. When the two lines cross, that is grid parody. Except, both have momentum, where the carbon fuels will continue to go up, while the PV continues to go down. That will be a glorious day, as it means that it is game over for the dirty carbon based energies.

Also, all nations of the world really need to start putting a price on the external costs these carbon based energies are producing, as well as take away their subsidies. They\'ve had a free ride for way too long.

Facebook User

Thats all well and good but the problem is not with efficiency it is with the cost. Get the cost down and solar will be worth while, but there is no point having 40% efficient pannels if they are not affordable.

Mark Lycett

Bringing any new advancement to the actual commercial stage, easily available in the market will be the true step forward. The same basic solar panels are being used for so many years, despite all the news of better efficiency panels. Price will fall eventually, but the new stuff is not there, and the old technology came from the space program.

Dawar Saify

Start cheap and small to saturate the market. Think accessories such as batteries before architectural structure.

Jeremy Buchstein

Grid \"parody\"?

Parody: something so badly done as to seem an intentional mockery; travesty (Collins Dictionary).

Seems very appropriate for the solar industry!

I think, Chris Amar, you mean parity, not parody.

Doug MacLeod already has a commercial application for this technology. By putting PV under Dynamic Spin, we automatically create this "shadow state." We did not use this terminology before, but this is exactly what is happening. Here is a 3 minute video that explains it:

Robert Styler
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