- Spin-flip metal complexes capture 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 devices
Japanese researchers have found a way to capture extra energy from sunlight using a metal-based system that reduces heat losses 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 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 part of the available energy ends up usable, leaving scientists hunting for ways to squeeze more output from the same incoming light.
One long-known ceiling comes from the mismatch between photon energies and how semiconductors respond, which means some photons fail to trigger electrons while others lose excess energy as heat.
This efficiency cap, known as the Shockley–Queisser limit, has pushed researchers to explore methods that reuse lost energy instead of letting it dissipate.
“We have two main strategies to break through this limit,” said Yoichi Sasaki, Associate Professor at Kyushu University’s Faculty of Engineering. “One is to convert lower-energy infrared photons into 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 the researchers as a “dream technology” for light conversion, plays a central role in the experiment because it allows one high-energy excitation to split into two lower-energy ones, theoretically doubling the number of usable energy carriers.
Capturing those duplicated excitons has been the harder problem, since competing energy transfer processes can redirect energy before it becomes useful.
The team addressed that 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 occurs,” said Sasaki. “We therefore 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 more energy carriers were generated than incoming photons absorbed under laboratory conditions.
Results remain limited to solution testing rather than full solar devices, meaning practical application still depends on translating the chemistry into solid materials compatible with 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 real 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.
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