Researchers have officially shattered the “physical ceiling” of solar energy conversion. By employing a revolutionary “spin-flip” emitter, a joint team from Kyushu University and Johannes Gutenberg University (JGU) Mainz has achieved a quantum yield of 130%.
This effectively proves that a solar system can generate more energy carriers than the number of photons it absorbs.
Breaking the “one-to-one” rule
For decades, solar technology has been hampered by the Shockley–Queisser limit. In traditional solar cells, the process is like a relay race: one photon strikes a semiconductor and excites exactly one electron. Any excess energy from high-energy photons (like blue light) is typically lost as wasted heat.
The new method utilizes Singlet Fission (SF)—often called a “dream technology”—to bypass this limitation.
In SF, a single high-energy “singlet” exciton is split into two lower-energy “triplet” excitons. Theoretically, this allows one photon to do the work of two.
The “spin-flip” innovation
While the concept of singlet fission isn’t new, capturing those “multiplied” excitons has proven nearly impossible. Usually, a process called Förster resonance energy transfer (FRET) “steals” the energy before it can be harvested.
To solve this, the research team developed a specialized molybdenum-based metal complex. This “spin-flip” emitter is designed to ignore the wasteful FRET process through selective harvesting.
By flipping the spin of an electron during light absorption, the complex achieves spin alignment to become the perfect “catcher” for the triplet energy produced by fission.
As a result of pairing this complex with tetracene-based materials, the team achieved a 130% quantum yield, meaning roughly 1.3 molybdenum complexes were excited for every single photon absorbed.
“We therefore needed an energy acceptor that selectively captures the multiplied triplet excitons after fission,” explained Associate Professor Yoichi Sasaki of Kyushu University in a press release.
“By carefully tuning the energy levels, the researchers suppressed the wasteful FRET process, allowing the multiplied excitons from SF to be selectively extracted,” added the press release.
Beyond the proof of concept
The collaboration was sparked by Adrian Sauer, a JGU Mainz exchange student who introduced the Kyushu team to materials long studied in Germany. While the current success was achieved in a solution-based environment, the implications are vast.
Traditional solar cells typically operate on a one-photon to one-electron transfer ratio with a maximum quantum yield of 100%. But this new singlet fission method enables a potential one-to-two transfer and has already reached a 130% yield with a theoretical limit of 200%.
In addition to this, while traditional cells suffer from high heat loss and rely on standard semiconductors, this innovation maintains low heat loss by using specialized molybdenum-based “spin-flip” emitters.
Transitioning into solid state
The researchers are now moving toward transitioning this technology into the solid state. The goal is to integrate these molecular “multipliers” into working solar cells, LEDs, and even next-generation quantum computers.
If successful, this could lead to ultra-high-efficiency panels that produce significantly more electricity from the same amount of sunlight, drastically accelerating the global transition away from fossil fuels.
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