Breakthrough in Solar Energy Efficiency: Exceeding the Shockley-Queisser Limit

A collaborative research effort between Kyushu University in Japan and Johannes Gutenberg University (JGU) Mainz in Germany has led to a significant advancement in solar energy technology, achieving a quantum yield of 130%. This breakthrough utilizes a novel “spin-flip” emitter, allowing solar cells to generate more energy carriers than the number of photons absorbed, effectively surpassing the long-standing Shockley-Queisser limit of 100%.

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Traditional solar cells operate on a one-photon to one-electron transfer ratio, where excess energy from high-energy photons is typically lost as heat. The new method employs singlet fission (SF), a process where a single high-energy exciton splits into two lower-energy triplet excitons, theoretically doubling the energy output from each absorbed photon. Associate Professor Yoichi Sasaki of Kyushu University explains, “We have two main strategies to break through this limit... to use SF to generate two excitons from a single exciton photon.”

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However, capturing these multiplied excitons has been challenging due to Förster resonance energy transfer (FRET), which can siphon off energy before it can be harvested. The research team addressed this by developing a molybdenum-based spin-flip emitter that selectively captures the triplet excitons produced during SF, effectively mitigating energy loss from FRET.

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The collaboration was sparked by Adrian Sauer, a graduate student from JGU Mainz, who introduced the Kyushu team to relevant materials. By pairing the molybdenum complex with tetracene-based materials, the researchers achieved a quantum yield of approximately 130%, meaning that for every photon absorbed, about 1.3 molybdenum complexes were activated. This result confirms that the system can generate and harvest more energy carriers than photons received.

Spin-flip emitter harvests doubled excitons for higher solar cell efficiency

While the current findings are still in the proof-of-concept stage, the implications are vast. The researchers aim to transition this technology into solid-state systems, which could lead to the development of ultra-high-efficiency solar panels, LEDs, and even next-generation quantum technologies. If successful, this innovation could significantly accelerate the global transition away from fossil fuels, enhancing the role of solar energy in combating climate change.

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Despite the promising results, some experts remain cautious about the scalability and practical application of this technology. Concerns exist regarding the efficiency of integrating these materials into existing solar cell architectures and the long-term stability of the new systems.

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The research team plans to further explore the integration of the spin-flip emitter and singlet fission materials into solid-state solar cells, aiming to optimize energy transfer and enhance overall efficiency. This next phase will be crucial in determining the viability of this technology for widespread use in renewable energy applications.

Spin-flip emitter harvests doubled excitons for higher solar cell efficiency

• “We therefore needed an energy acceptor that selectively captures the multiplied triplet excitons after fission.” — Yoichi Sasaki, Associate Professor, Kyushu University

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• “We could not have reached this point without the Heinze group from JGU Mainz,” — Yoichi Sasaki, Associate Professor, Kyushu University

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This breakthrough in solar technology represents a significant step forward in energy efficiency, potentially transforming the landscape of renewable energy.

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