A group of scientists from Japan and Germany has presented a strong>experimental system that promises to revolutionize the efficiency of solar energyThe work, authored by researchers from Kyushu University and Johannes Gutenberg University Mainz, points to a way to extract much more electricity from the same amount of light, something that has been pursued for decades in the photovoltaic field.
The research, published in the Journal of the American Chemical Society, describes an approach that, if confirmed in real devices, For now, everything has been tested under strictly laboratory conditions, but the potential impact on markets like Spain or Europe does not go unnoticed, especially in a context of strong commitment to renewables.
A physical limit that hinders the efficiency of solar panels
Current photovoltaic solar energy is based on semiconductor materials, primarily silicon, which convert photons into electricity. However, this process encounters a well-known barrier: Shockley-Queisser limitThis physical principle dictates the extent to which a single-junction cell can transform incident radiation into useful energy.
In practice, A significant portion of the photons that reach the panel are not usedSome cells have very little energy and don't even generate an electrical charge; others, at the opposite extreme, provide more energy than the material can handle, and the excess is dissipated as heat. The result is that, generally speaking, conventional cells only convert about a third of the solar energy they receive into electricity.
This gap between what comes from the sun and what is actually used is one of the industry's biggest challenges. “We know that There is available energy that we are not using.“The key question was how to increase the energy obtained without needing more panel surface area or skyrocketing costs,” explains Associate Professor Yoichi Sasaki of Kyushu University’s College of Engineering, in statements collected by the team.
In a context like the European one, where the availability of space and integration into roofs and facades Achieving higher yields per square meter is becoming a determining factor, something that interests electric companies, homeowners, and public administration alike.
Singlet fission: multiplying excitons with a single photon
The advance of the Kyushu and Mainz team is based on a phenomenon known as singlet fissionIn broad terms, this is a process by which a high-energy photon, instead of producing a single electronic excitation (an exciton), generates two. This multiplies the number of energy carriers generated from the same incident light.
In a standard solar panel, each photon that exceeds the minimum energy threshold results in a single exciton, and anything beyond that threshold is, so to speak, "burned off" as heat. With singlet fission, a single photon can produce two lower-energy excitonswhich can be used much more efficiently in the conversion to electricity.
For years, this idea has been considered promising but difficult to put into practice. The main headache was that The additional excitements faded in extremely short times.before the system managed to capture them. Thus, the theoretical benefit never fully translated into a real increase in performance.
The new study addresses precisely that point: how to prevent that extra energy from being lost along the way. To do this, the scientists have used specially designed materials that act as “intermediaries,” allowing the triplet states generated by singlet fission to be retained long enough to be harnessed.
The role of the molybdenum-based spin-rotation emitter
The centerpiece of this approach is a spin-rotation emitter made from a molybdenum compoundThis material functions as a highly selective energy acceptor: its mission is to preferentially detect and capture triplet excitons that originate after singlet fission, limiting alternative loss pathways.
In conventional photovoltaic devices, there is a competing mechanism called Förster resonance energy transfer (FRET)which can "steal" energy before exciton multiplication translates into payload. The design proposed by Sasaki's team seeks to circumvent this problem by very precisely controlling the material that receives that energy.
According to the researchers, The selection of the energy acceptor is crucialIf it does not preferentially capture these multiplied triplet states, the advantage of singlet fission is diminished. The molybdenum compound has been chemically tuned to make the process as efficient as possible, reducing heat losses and maintaining the system at relatively lower temperatures during operation.
In laboratory tests, tetracene solutions were used as the medium where singlet fission occurs, combined with the molybdenum spin-flip emitter. This controlled environment has allowed closely monitor how excitons are generated and transferredand accurately measure the returns achieved.
Quantum yields exceeding 100% under laboratory conditions
The experimental results are striking: the researchers report that quantum yields between 110% and 130% in the tests carried out. This means that more energy carriers (excitons) are obtained than would correspond to the number of photons absorbed, something that breaks with the usual intuition about photovoltaic conversion.
It is worth clarifying that a quantum efficiency above 100% does not imply generating more energy than is input, but Make better use of available energy by dividing it into more usable excitations.Total energy is conserved, but distributed in a way that is more favorable for the photovoltaic device.
The study demonstrates that, at least in a controlled chemical environment, It is possible to circumvent some of the limitations imposed by the Shockley-Queisser limit through these types of advanced processes. From a scientific point of view, it confirms that the concept of singlet fission is more than just a theoretical curiosity.
Furthermore, the system tends to maintain lower operating temperatures than many current cells, which in the long term could have repercussions on less material degradationTemperature is a key factor in the lifespan of solar panels, even in sunny climates like those in southern Europe.
From dissolution to solar panel: the great challenge still pending
Despite the positive data obtained, those responsible for the project themselves insist that the technology It is still in a very early stage.All tests have been carried out in liquid solution, not in solid devices comparable to a commercial photovoltaic module.
The next step, according to the team, involves transferring this chemistry to solid structures that can be integrated into real solar cells. This involves developing material layers and architectures where singlet fission and exciton capture by the molybdenum emitter remain efficient and stable over time.
That leap is not trivial. It would be necessary to guarantee that The behavior observed in the laboratory is preserved when scaling up the technologyThis applies both to size and operating conditions (actual solar radiation, temperature changes, humidity, day/night cycles, etc.). Furthermore, these new materials would need to be compatible with existing manufacturing processes in the industry.
Even so, the researchers are reasonably confident that the concept can evolve into more practical structures. Professor Sasaki admits that “we are in an initial phase,” but emphasizes that What has long been a purely theoretical idea is beginning to show that it can work when the system is properly designed.
Potential impact on the European and Spanish solar market
If such a system were to be implemented in commercial panels, the implications would be far-reaching. For Europe, where the energy roadmap sets ambitious renewable energy targets, to have more efficient modules without needing to increase the installed surface area It could facilitate the achievement of decarbonization goals.
In countries like Spain, with high solar irradiation and a strong growth in self-consumptionA technology that delivers more energy per panel would help Optimize residential roofs, industrial buildings and large photovoltaic plantsIn dense urban areas, where every square meter of roof space counts, that increase in performance can make all the difference in the viability of many projects.
Furthermore, the possibility of reducing the cost per kilowatt-hour generated would bring solar energy even closer to residential users and small businesses, strengthening its competitiveness against other sources. If these types of systems can be stabilized and manufactured on a large scale, European industry could benefit from a significant technological advantageprovided that you actively participate in its development and integration.
For the moment, progress is focused on basic and applied laboratory research, but it is expected that working groups and R&D centers in the European Union will closely follow this line of research. It would not be surprising if, in the coming years, collaborative projects between Asian and European universities emerge to adapt singlet fission and molybdenum emitters to specific panel architectures already in use on the continent.
Beyond photovoltaics: possible additional applications
The researchers also point out that the such fine control of exciton behavior This could open the door to innovations in other optoelectronic devices. Among the candidates are displays and lighting systems based on OLED technology, where excitonic energy management directly influences brightness, power consumption, and lifespan.
By learning to direct and multiply excitonic energy with less loss, it might be possible to conceive more efficient devices with less heat generationThis is an important aspect in both consumer products and professional applications. The same logic that allows us to overcome some of the losses in a photovoltaic system can be applied, with adaptation, to other environments where light and matter interact in a similar way.
In the field of sensors, advanced photonics, or even certain light-assisted chemical conversion processes, having materials that better manage excited states could also represent a qualitative leap. However, in all these cases, as with solar energy, further research will be needed. to travel a long way from laboratory demonstration to commercial products.
However, the message this work leaves is clear: There is room for improvement in the way we currently harness sunlight.The singlet fission approach combined with spin-rotation emitters appears to be a promising avenue. If the scientific and industrial community manages to translate these advances into robust and affordable technologies, the way solar energy is designed and deployed in Spain, Europe, and the rest of the world could change considerably in the coming decades.
