Solar cell polymers with multiplied electrical output

Solar cell polymers with multiplied electrical output
Postdoctoral fellow Erik Busby and Matt Sfeir with opticalequipment they used to study charge carrier production in organicphotovoltaic polymers at Brookhaven Lab's Center for FunctionalNanomaterials. Credit: Brookhaven National Laboratory

One challenge in improving the efficiency of solar cells is that some of the absorbed light energy is lost as heat. So scientists have been looking to design materials that can convert more of that energy into useful electricity. Now a team from the U.S. Department of Energy's Brookhaven National Laboratory and Columbia University has paired up polymers that recover some of that lost energy by producing two electrical charge carriers per unit of light instead of the usual one.

"Critically, we show how this multiplication process can be made efficient on a single molecular polymer chain," said physicist Matthew Sfeir, who led the research at Brookhaven Lab's Center for Functional Nanomaterials, a DOE Office of Science User Facility. Having the two charges on the same molecule means the light-absorbing, energy-producing don't have to be arrayed as perfect crystals to produce extra electrical charges. Instead, the self-contained materials work efficiently when dissolved in liquids, which opens the way for a wide range of industrial scale manufacturing processes, including "printing" solar-energy-producing material like ink.

The research is published as an Advance Online Publication in Nature Materials, January 12, 2015.

The concept of producing two charges from one unit of light is called "." (Think of the fission that splits a single biological cell into two when cells multiply.) Devices based on this multiplication concept have the potential to break through the upper limit on the efficiency of so-called single junction , which is currently around 34 percent. The challenges go beyond doubling the electrical output of the solar cell materials, because these materials must be incorporated into actual current-producing devices. But the hope is that the more-efficient current-generating materials could be added on to existing solar cell materials and device structures, or spark new types of solar cell designs.

Most singlet fission materials explored so far result in twin charge carriers being produced on separate molecules. These only work well when the material is in a crystalline film with long-range order, where strong coupling results in an additional charge being produced on a neighboring molecule. Producing such high quality crystalline films and integrating them with solar cell manufacturing complicates the process.

Producing the twin charges on a single polymer molecule, in contrast, results in a material that's compatible with a much wider variety of industrial processes.

The materials were designed and synthesized by a Columbia University team led by Professor Luis Campos, and analyzed at Brookhaven using specialized tools at the CFN and in the Chemistry Department. For Sfeir and Campos, the most fascinating part of the interdisciplinary project was exploring the electronic and chemical requirements that enable this multiplication process to occur efficiently.

"We expect a significant leap in the development of third-generation, hot-carrier solar cells," said Campos. "This approach is especially promising because the materials' design is modular and amenable to current synthetic strategies that are being explored in second-generation ."

Details of the materials' analysis

At the CFN, Sfeir and Erik Busby (a postdoctoral fellow) used time-resolved optical spectroscopy to induce and quantify singlet fission in the various polymer compositions using a single laser photon. Xiaoyang Zhu of Columbia helped to understand the data and interpret results.

"We put light energy into a material with a laser pulse and watch what happens to that energy using a series of weaker light pulses - somewhat analogous to taking snapshots using a camera with a very fast shutter," Sfeir said.

The team also studied the same process using "pulse radiolysis" in collaboration with John Miller, who runs the Laser-Electron Accelerator Facility.

"The differences observed between these two experiments allowed us to unambiguously identify singlet fission as the primary process responsible for the production of these twin charges," Sfeir said.

With Qin Wu, the team also used a powerful computer cluster at the CFN to model these materials and understand the design requirements that were necessary for singlet fission to take place.

"The ideas for this project and supervision of the work were really shared between Brookhaven and Columbia," Sfeir said. "It's a great example of the kind of collaborative work that takes place at DOE user facilities like the CFN."

The next steps for the CFN-Columbia team will be to test a large class of materials using the design framework they've identified, and then integrate some of these carbon-based polymer materials into functioning solar cells.

"Even though we have demonstrated the concept of multiplication in single molecules, the next challenge is to show we can harness the extra excitations in an operating device. This may be in conventional bulk type solar cells, or in third-generation concepts based on other inorganic (non-carbon) nanomaterials. The dream is to build hot-carrier solar cells that could be fully assembled using solution processing of our organic singlet fission materials."

Explore further

Two for one in solar power

More information: A design strategy for intramolecular singlet fission mediated by charge-transfer states in donor–acceptor organic materials, Nature Materials, DOI: 10.1038/nmat4175
Journal information: Nature Materials

Citation: Solar cell polymers with multiplied electrical output (2015, January 12) retrieved 18 April 2019 from
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Jan 12, 2015
If we covered the massive Containment vessels of the nukes, we could make them actually productive, . . with NO high-level waste!

The owners of Rancho Seco closed their nuke and replaced it with conservation and PVs.

Jan 12, 2015
he owners of Rancho Seco closed their nuke and replaced it with conservation and PVs.

And a 600 MW gas-fired plant to actually make the electricity.

Jan 12, 2015
I think Eikka should look into the alternative energy and conservation programs of SMUD.

Jan 12, 2015
I think Eikka should look into the alternative energy and conservation programs of SMUD.

I did the last time you started ranting about the Rancho Seco.

The nuclear powerplant was 913 MWe with a 39% average capacity factor, which is approx 360 MW actual average output.

After the plant was taken offline and dismantled, the site was built with 3.2 MWp of solar PV with a capacity factor of approximately 14% which is approximately 0.5 MW actual average output. In other words, about a thousandth of what the nuclear powerplant provided even when it was malfunctioning half the time.

The missing power was actually bought from neighboring utilities at a higher cost. Then in 2006, PG&E started the 500 MW gas powered plant just a couple miles south from the old nuclear plant. Then in 2010 they started another 660 MW gas powered plant in Colusa County.

Jan 12, 2015
Meanwhile, from the 3.2 MWp of solar PV they installed in 1986, PG&E has expanded to about 100 MWp, with an average actual output around 15-20 MW.

Not very much.

These figures are relatively hard to come by because the utilities and organizations are curiously averse to publishing any actual figures on their websites. They only talk of powering so and so many homes, or percentages of something which includes all the power they buy out of state as well as the old hydroelectric plants they've owned since the 1960's.

The truth of the matter is that the vast majority of renewable power the SMUD or PG&E has is old high head hydro. It's "always" been there, and they're just now started to use it to stuff their portfolio to make it look more impressive.

Jan 12, 2015
SMUD's existing and contracted supply by renewable resource type in 2012 was:

Wind power ~80 MW
Biomass ~100 MW
Solar ~20 MW
Small hydro ~32 MW
Biogas ~22 MW
Biomethane ~26 MW

Total: 280 MW

Note: calculated out of supplied annual total energy.

Source: California Energy Commission

Jan 12, 2015
Californian Total Electricity System Power in 2013:

In-state generation (percentage of)

Solar ~490 MW (2.15%)
Wind ~1,500 MW (6.35%)

Natural gas ~13,800 MW (60.50%)


And so forth... so what was the point you wanted to make about the alternative energy programs, gkam?

Jan 12, 2015
The point is they have already captured much territory from coal and nukes, and gas will be our bridge to greater penetration of the technologies. You may not be aware of the typical life cycle of power plants, but they are long-term affairs.

But you can put your money where your mouth is, and buy into the nuclear and coal plants now being spun off in Europe by their owners and operators.

Jan 12, 2015
The point is they have already captured much territory from coal and nukes, and gas will be our bridge to greater penetration
No the point is
The owners of Rancho Seco closed their nuke and replaced it with conservation and PVs
-you were wrong. Again.

Jan 12, 2015
I wonder which nukes will be the next to close. They are acknowledged monsters and such huge liabilities utilities now need government-guaranteed loans for the taxpayer to pay when they go belly up.

Keep your eyes on the two Votgle plants in Georgia. They are the Edsels of the nuclear business, and perhaps the last of nuclear power in the US.

Let's face it: Using 3,000,000 degree Neutrons to boil water is ridiculous!

Jan 12, 2015
Let's look to that hotbed of radical leftist thought, Forbes, to see what the future looks like for nuclear power.




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