- Spin-flip metal complexes capture duplicate excitons produced by singlet fission
- Proof-of-concept experiments achieved quantum yields between 110% and approximately 130%
- Solid-state integration remains necessary before use in practical solar devices
Japanese researchers have found a way to capture additional energy from sunlight using a metal-based system that reduces heat losses during conversion.
The work focuses on a chemical structure known as a spin-flip emitter, built from molybdenum, which captures the multiplied energy created during a process called singlet fission.
The research was carried out by Kyushu University in Japan, in collaboration with Johannes Gutenberg University (JGU) Mainz in Germany. The findings were published in the Journal of the American Chemical Society.
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Energy easily ‘stolen’
Solar cells already convert sunlight into electricity, but only a portion of the available energy ends up being usable, leaving scientists looking for ways to make more use of the same incoming light.
One long-known ceiling comes from the mismatch between photon energies and the way semiconductors respond, meaning that some photons fail to activate electrons while others lose excess energy as heat.
This efficiency limit, known as the Shockley-Queisser limit, has led researchers to explore methods that reuse lost energy rather than letting it dissipate.
“We have two main strategies to overcome this limit,” said Yoichi Sasaki, an associate professor at the Faculty of Engineering at Kyushu University. “One is to convert lower energy infrared photons to higher energy visible photons. The other, what we explore here, is to use SF to generate two excitons from a single exciton photon.”
Singlet fission, described by researchers as a “dream technology” for light conversion, plays a central role in the experiment because it allows one high-energy excitation to be split into two lower-energy ones, theoretically doubling the number of usable energy carriers.
Capturing those duplicate excitons has been the most difficult problem, since competing energy transfer processes can redirect the energy before it is useful.
The team addressed that bottleneck by combining singlet fission materials with a molybdenum-based near-infrared spin-flip emitter tuned to absorb specific triplet energy states.
“Energy can be easily ‘stolen’ by a mechanism called Förster resonance energy transfer (FRET) before multiplication occurs,” Sasaki said. “Therefore, we needed an energy acceptor that selectively captures the multiplied triplet excitons after fission.”
Experiments using tetracene-based materials in solution produced quantum yields ranging from just over 110% to about 130%, meaning that more energy carriers were generated than the incoming photons absorbed under laboratory conditions.
Results remain limited to testing solutions rather than complete solar devices, meaning practical application still depends on translating the chemistry into solid materials compatible with the working panels.
Future work will focus on combining these materials into solid-state systems where energy transfer efficiency can be tested under conditions closer to actual solar cell operation.
The researchers point to possible applications beyond solar panels, including lighting technologies such as OLED, where managing exciton behavior plays a key role in performance.
Through Kyushu University
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