+44 (0)24 7671 8970
More publications     •     Advertise with us     •     Contact us
 
Loading...
{megaLeaderboard}
{normalLeaderboard}
News Article

Singlet fission research reveals efficiency boosts up to 30%

News

A perspective article published last month by University of California, Riverside chemists in the Journal of Physical Chemistry Letters was selected as an Editors Choice, an honour only a handful of research papers receive.  The perspective reviews the chemists' work on "singlet fission," a process in which a single photon generates a pair of excited states. This 1->2 conversion process, as it is known, has the potential to boost solar cell efficiency by as much as 30 percent.

Applications of the research include more energy-efficient lighting and photodetectors with 200 percent efficiency that can be used for night vision. Biology may use singlet fission to deal with high-energy solar photons without generating excess heat, as a protective mechanism.

Currently, solar cells work by absorbing a photon, which generates an exciton, which subsequently separates into an electron-hole pair.  It is these electrons that become solar electricity.  The efficiency of these solar cells is limited to about 32 percent, however, by what is called the "Shockley-Queisser Limit."  Future solar cells, also known as "Third Generation" solar cells, will have to surpass this limit while remaining inexpensive, requiring the use of new physical processes. Singlet fission is an example of such a process.

"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," said Christopher Bardeen, a professor of chemistry, whose lab led the research. "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."

When a photon is absorbed, its energy takes the form of an exciton inside the material. Bardeen explained that excitons come in two "flavors," defined by the electron spins in them.  One flavor is singlet, where all spins are paired.  The other flavor is triplet, where two electrons are unpaired.  In organic semiconductors, these two types of excitons have different energies.

"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," Bardeen said.  "Thus, you could have a 200 percent yield of excitons "” and hopefully, electrons "” per absorbed photon."

He explained that the Shockley-Queisser Limit involves photon absorption to create an exciton, which is basically a bound electron (- charge) and hole (+ charge) pair. In order to get useful electron flow (photocurrent), these excitons must be dissociated. Ideally, one exciton produces one electron (hole) and thus current to run, say, a light bulb.

To absorb a photon, the photon energy has to be greater than the bandgap of the semiconductor, so you already miss part of the solar spectrum," Bardeen said.  "But if you absorb a photon with energy higher than the bandgap, it has too much energy, and that excess energy is usually wasted as heat.  The trick is to take that high energy exciton and split the energy into two excitons, rather than dissipating it as heat."

Bardeen explained that the singlet exciton spontaneously splits into the two triplets, through a mechanism that is still under active investigation.

"The exact mechanism is unknown, but it does happen quickly, at the sub-nanosecond timescale,  and with high efficiency," he said.  "Our work has shown that it is very sensitive to the alignment and position of the two molecules,  at least two are required, since we have two excitons,  involved in singlet fission. Recent work at MIT has already demonstrated an organic photovoltaic cell with more than 100 percent external quantum efficiency based on this effect.  It may be possible to integrate this effect with inorganic semiconductors and use it to raise their efficiencies."

Next, Bardeen's lab will look for new materials that exhibit singlet fission, figure out how to take the triplet excitons and turn them into photocurrent efficiently, and look at how the spin properties of the electrons affect the exciton dynamics.

The research was supported by a grant to Bardeen from the National Science Foundation. He was joined in the research by Geoffrey B. Piland, Jonathan J. Burdett and Robert J. Dillon at UC Riverside.

Journal Reference: Geoffrey B. Piland, Jonathan J. Burdett, Robert J. Dillon, Christopher J. Bardeen. Singlet Fission: From Coherences to Kinetics. The Journal of Physical Chemistry Letters, 2014; 5 (13): 2312 DOI: 10.1021/jz500676c

 

Geoffrey Piland (left) is a graduate student working with Christopher Bardeen (right). They are two of the four coauthors of the perspective article.Photo credit: Barden Lab, UC Riverside.


Top image:Singlet fission is a process in which a single photon generates a pair of excited states. This 1->2 conversion process has the potential to boost solar cell efficiency by as much as 30 percent. Image credit: Bardeen Lab, UC Riversi


 

 


 

Schletter Group: 48 MWp Project in Italy
ENCAVIS Acquires Two More Solar Parks In Spain and Surpasses The Planned Expansion
Maximum profitability with KACO advanced technology for complex solar roofs
Enviromena wins contract to re-power three major solar farms ahead of the summer energy peak
New Swansea University Collaboration to Support Sustainable, Locally Manufactured Solar PV
New Swansea University Collaboration to Support Sustainable, Locally Manufactured Solar PV
Next2Sun Builds World's Largest Vertical PV Plant at Frankfurt Airport
DNV Publishes Bankability Study of Solcast Satellite Irradiance Data
Steel company SSAB switches to fossil-free energy in Italy with PV solution from Solnet
janom Investments enters the Croatian solar energy industry by investing in a 30 MW power plant project
Trina Solar Vertex S+ 505W n-type dual-glass modules enter mass production
BayWa r.e. and 3E sign partnership agreement for monitoring & analytics of global PV portfolio
Accelerating Spain's Energy Transformation: LONGi to supply Naturgy with 1 million modules in new deal
NTR announces corporate PPA with Almac Group to buy energy from Murley Wind Farm, Northern Ireland
Oxford PV sets new solar panel efficiency world record
Order Intake for the Construction of Wind Turbines in Turkey
Trilantic Europe acquires stake in AEROCOMPACT Group
Octopus Energy makes solar farm debut in Germany
Austria-based KOGA Energy, a solar EPC solutions provider, has kicked off.
Exus to acquire 625MW New Mexico solar portfolio
Capcora Accompanies SUSI Partners In Raising Senior Debt For a Polish Renewables Portfolio
Qualitas Energy acquires a 96 MW wind energy project pipeline in Germany
Nordex Group receives orders from the UK for approx. 150 MW
Trina Solar gains EPD certification from UL Solutions and EPDItaly for industry leading modules
Mandarin Oriental Hyde Park, London instals innovative solar tech to decarbonise heating
Efficiency First: The Road to Electrification
SCHLETTER Supplies Austria's Largest PV Roof System
E.ON partners with UK renewable heat innovator Naked Energy
Sonnedix signs innovative EUR500 million loan facility to finance construction of its renewable electricity pipeline in Europe and UK
Construction begins on Glennmont and Ørsted’s Borkum Riffgrund 3 offshore wind farm in Germany
ABB shores up reliable power supply at Southeast Asia’s largest floating solar plant
Sonnedix starts construction of 300MW UK solar PV portfolio

×
Search the news archive

To close this popup you can press escape or click the close icon.
Logo
×
Logo
×
Register - Step 1

You may choose to subscribe to the Solar + Power Magazine, the Solar + Power Newsletter, or both. You may also request additional information if required, before submitting your application.


Please subscribe me to:

 

You chose the industry type of "Other"

Please enter the industry that you work in:
Please enter the industry that you work in: