- Spin-flip metal complexes trap duplicated excitons produced through singlet fission
- Proof-of-concept experiments reached over 110% to about 130% quantum yield
- Solid-state integration remains necessary before use in practical solar cells
Japanese researchers have found a way to capture extra energy from sunlight using a metal-based system that reduces heat loss during conversion.
The work centers on a chemical structure known as a spin-flip emitter, built from molybdenum, that captures 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 results were published in 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 squeeze more output from the same incoming light.
A long-known ceiling comes from the mismatch between photon energies and how semiconductors react, meaning that some photons fail to eject electrons while others lose excess energy as heat.
This efficiency limit, known as the Shockley-Queisser limit, has pushed researchers to explore methods that recycle lost energy instead of letting it dissipate.
“We have two main strategies to break through this limit,” said Yoichi Sasaki, an associate professor at Kyushu University’s Faculty of Engineering. “One is to convert lower-energy infrared photons to higher-energy visible photons. The other, what we’re exploring here, is to use SF to generate two excitons from a single exciton photon.”
Singlet fission, described by the researchers as a “dream technology” for light conversion, plays a central role in the experiment because it allows a high-energy excitation to split into two lower-energy ones, theoretically doubling the number of usable energy carriers.
Trapping these duplicated excitons has been the more difficult problem, as competing energy transfer processes can divert energy before it becomes useful.
The team addressed this bottleneck by pairing singlet fission materials with a molybdenum-based near-infrared spin-flip emitter tuned to absorb specific triplet energy states.
“The energy can be easily ‘stolen’ by a mechanism called Förster resonance energy transfer (FRET) before multiplication takes place,” said Sasaki. “We therefore needed an energy acceptor that selectively captures the multiplied triplet excitons after fission.”
Experiments with tetracene-based materials in solution produced quantum yields ranging from just over 110% to about 130%, meaning that more energy carriers were generated than incoming photons absorbed under laboratory conditions.
The results remain limited to solution tests rather than complete solar devices, meaning that practical application still depends on translating the chemistry into solid materials compatible with working panels.
Future work will focus on combining these materials in solid state systems where the energy transfer efficiency can be tested under conditions closer to real solar cell operation.
The researchers point to possible applications beyond solar panels, including lighting technologies such as OLED, where control of exciton behavior plays a key role in performance.
Via Kyushu University
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