Scientists may have found a way to squeeze more energy out of sunlight than ever thought possible—breaking a long-standing “efficiency ceiling” in solar technology.
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A new “energy-multiplying” solar breakthrough could push efficiency beyond 100% and transform how we capture sunlight.
Solar energy is widely seen as a key tool in reducing reliance on fossil fuels and slowing climate change. The Sun delivers a vast amount of energy to Earth every second, but today’s solar cells can only capture a small portion of it. This limitation comes from a so-called “physical ceiling” that has long been considered unavoidable.
Breakthrough Spin-Flip Technology Boosts Solar Efficiency
In a study published today (March 25) in the Journal of the American Chemical Society, researchers from Kyushu University in Japan, working with collaborators at Johannes Gutenberg University (JGU) Mainz in Germany, introduced a new approach to overcome this barrier. They used a molybdenum-based metal complex known as a “spin-flip” emitter to capture extra energy through singlet fission (SF), often described as a “dream technology” for improving light conversion.
This method achieved an energy conversion efficiency of about 130%, exceeding the traditional 100% limit and pointing toward more powerful future solar cells.
How Solar Cells Work and Why Energy Is Lost
Solar cells generate electricity when photons from sunlight strike a semiconductor and transfer their energy to electrons, setting them in motion and producing an electric current. This process can be visualized as a relay, where energy is passed along particle by particle.
However, not all sunlight contributes equally. Low-energy infrared photons lack the power to excite electrons, while high-energy photons, such as blue light, lose excess energy as heat. Because of this imbalance, solar cells can only utilize roughly one-third of incoming sunlight. This restriction is known as the Shockley–Queisser limit and has posed a major challenge for decades.
Solar cells generate electricity when photons from sunlight strike a semiconductor and transfer their energy to electrons, setting them in motion and producing an electric current. This process can be visualized as a relay, where energy is passed along particle by particle.
However, not all sunlight contributes equally. Low-energy infrared photons lack the power to excite electrons, while high-energy photons, such as blue light, lose excess energy as heat. Because of this imbalance, solar cells can only utilize roughly one-third of incoming sunlight. This restriction is known as the Shockley–Queisser limit and has posed a major challenge for decades.
Using Singlet Fission To Multiply Energy
“We have two main strategies to break through this limit,” says 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.”
Under typical conditions, one photon produces just one spin-singlet exciton after excitation. With SF, that single high-energy exciton can split into two lower-energy spin-triplet excitons, potentially doubling the usable energy. While materials like tetracene can support this process, efficiently capturing the resulting excitons has remained difficult.
Overcoming Energy Loss From FRET
“The energy can be easily ‘stolen’ by a mechanism called Förster resonance energy transfer (FRET) before multiplication occurs,” Sasaki explains. “We therefore needed an energy acceptor that selectively captures the multiplied triplet excitons after fission.”
To solve this problem, the researchers turned to metal complexes, which can be precisely engineered at the molecular level. They identified a molybdenum-based “spin-flip” emitter that can effectively collect the energy produced during SF. In these molecules, an electron changes its spin during interactions with near-infrared light, allowing the system to absorb triplet energy efficiently.
By carefully adjusting energy levels, the team reduced losses from FRET and enabled selective extraction of the multiplied excitons.
“We have two main strategies to break through this limit,” says 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.”
Under typical conditions, one photon produces just one spin-singlet exciton after excitation. With SF, that single high-energy exciton can split into two lower-energy spin-triplet excitons, potentially doubling the usable energy. While materials like tetracene can support this process, efficiently capturing the resulting excitons has remained difficult.
Overcoming Energy Loss From FRET
“The energy can be easily ‘stolen’ by a mechanism called Förster resonance energy transfer (FRET) before multiplication occurs,” Sasaki explains. “We therefore needed an energy acceptor that selectively captures the multiplied triplet excitons after fission.”
To solve this problem, the researchers turned to metal complexes, which can be precisely engineered at the molecular level. They identified a molybdenum-based “spin-flip” emitter that can effectively collect the energy produced during SF. In these molecules, an electron changes its spin during interactions with near-infrared light, allowing the system to absorb triplet energy efficiently.
By carefully adjusting energy levels, the team reduced losses from FRET and enabled selective extraction of the multiplied excitons.
Collaboration and Experimental Results
“We could not have reached this point without the Heinze group from JGU Mainz,” Sasaki says. Adrian Sauer, a graduate student from the group visiting Kyushu University on exchange and the paper’s second author, brought the team’s attention to a material that has long been studied there, leading to the collaboration.
When combined with tetracene-based materials in solution, the system successfully harvested energy with quantum yields of around 130%. In practical terms, this means about 1.3 molybdenum-based metal complexes were activated for every photon absorbed, surpassing the conventional limit and demonstrating that more energy carriers were generated than incoming photons.
Future Applications in Solar and Quantum Technologies
This research introduces a new strategy for amplifying excitons, although it is still at an early proof-of-concept stage. The team plans to integrate the materials into solid-state systems to improve energy transfer and move closer to real-world solar cell applications.
The findings may also inspire further work combining singlet fission with metal complexes, with potential uses not only in solar energy but also in LEDs and emerging quantum technologies.
This research introduces a new strategy for amplifying excitons, although it is still at an early proof-of-concept stage. The team plans to integrate the materials into solid-state systems to improve energy transfer and move closer to real-world solar cell applications.
The findings may also inspire further work combining singlet fission with metal complexes, with potential uses not only in solar energy but also in LEDs and emerging quantum technologies.
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