This story was originally published by The Guardian and is reproduced here as part of the Climate Table partnership .
Solar cells have surpassed the 30 percent energy efficiency mark thanks to the innovations of many research groups around the world . According to one expert, this success makes this a "revolutionary" year and could accelerate the adoption of solar energy.
Solar cells today use silicon-based cells, but are fast approaching the maximum conversion of sunlight into electricity of 29 percent. At the same time, according to scientists, the rate of installation of solar energy must increase tenfold to overcome the climate crisis.
The breakthrough lies in adding a layer of perovskite, another semiconductor, on top of the silicon layer. It absorbs blue light from the visible spectrum, while silicon captures red light, increasing the total amount of light it captures. When more energy is absorbed per cell, the cost of solar electricity becomes cheaper and deployment can happen faster, helping to curb global warming.
Perovskite-silicon "tandem" cells have been studied for about a decade, but recent technical improvements have allowed them to overcome the 30 percent threshold. Experts say that if the scale-up of production of tandem cells goes smoothly, they could be commercially available within five years, about the same time that silicon-only cells reach their peak efficiency.
The two groups published details of their progress in efficiency in the journal Science on Thursday, and at least two groups are known to have exceeded 30 percent. "This is a revolutionary year," said Stefan de Wolff, a professor at the King Abdullah University of Science and Technology in Saudi Arabia. "It's amazing how fast things can go with so many groups."
The current efficiency record for silicon-only solar cells is 24.5% for commercial cells and 27% for laboratory cells. The latter cells can be close enough in practice to reach the theoretical maximum of 29 percent.
A group led by Steve Albrecht of the German Center for Materials and Energy in Berlin has published information on how they achieved efficiencies of up to 32.5% for silicon perovskite cells. Another group headed by Dr. Xin Yu Qi of the Swiss Federal Institute of Technology in Lausanne demonstrated an efficiency of 31.25% and said that tandem cells "have the potential for both high efficiency and low manufacturing costs."
"What these two groups are showing are really important developments," DeWolf said. His own group achieved an efficiency of 33.7% with a tandem cell in June, but the results have not yet been published in a journal. All performance indicators have been verified by independent experts.
"Exceeding the 30 percent threshold gives confidence that highly efficient and inexpensive photovoltaic systems will be brought to the market," said DeWolf. In 2022, the global solar energy capacity will reach 1.2 terawatts. "It is still necessary to increase the total capacity to about 75 TW by 2050 to avoid catastrophic global warming scenarios," he said.
The solar industry is also part of the race for high efficiency. China's LONGi, the world's largest solar panel maker, announced in June that it had reached 33.5%. "Reducing the cost of electricity remains a constant theme that drives the development of the photovoltaic industry," said Li Zheng, president of LONGi.
"The industry is growing very, very quickly," DeWolf said. "And I'm sure a lot of companies in China are working on that." According to him, Europe and the US should increase funding for research and development to continue and promote the acceleration of the use of solar energy.
All high-efficiency cells with efficiencies above 30 percent have so far been small, measuring 1 cm by 1 cm. Now they need to be scaled up to commercial cell sizes of 15 square meters. see
Large-scale work is already underway at UK-based Oxford PV, which in May announced a record 28.6% efficiency for commercial-sized cells. "Solar energy is already one of the most expensive and cleanest forms of energy, and our technology will make it even more affordable," said Chris Case, CTO of Oxford PV.
The Oxford photocell is created on the same production line as conventional silicon cells, greatly simplifying the large-scale production of tandem cells. According to DeWolf, tandem cells can be more expensive than single silicon cells, but they are only a fraction of the cost of manufacturing and installing solar cells.
One issue that remains to be resolved is how quickly tandem cells decay over time under real-world conditions. Today's solar cells still have 80 to 90 percent of their capacity after 25 years, and DeWolf said tandems should be able to match that, but so far there is only limited information on their longevity.
The basis for higher efficiency of tandem cells of the German and Swiss groups was the elimination of small defects on the surface of the perovskite layer. They allow some of the electrons emitted by solar photons to flow back to the perovskite instead of contributing to the cell's electrical current, thereby reducing its efficiency.
The solution was to place a layer of organic molecules between the perovskite and the conducting layer, where the current flows, compensating for the defects.
In particular, all the groups used different methods to solve the problem, which gave them more opportunities to find the best commercial design, DeWolf said. "There are still many opportunities for further development," he said. "I think the practical limit is above 35 percent."
Professor Rob Gross, Director of the UK Center for Energy Research, said: “Solar energy is already a cheap way to generate electricity and has a large resource base around the world. The cost reductions already achieved are the main reason why solar energy plays such a large role in low-carbon energy systems scenarios. Improving efficiency can increase solar energy production and thus help amplify this effect.”
There are other technologies, such as multi-junction cells, which can be as high as 47 percent efficient, but they are very expensive to manufacture and are only suitable for local use on space satellites or in high concentrations of sunlight. solar panels.
