In a big leap forward for renewable energy, solar power cells have surged beyond a critical threshold, achieving an unprecedented 30% energy efficiency milestone.
This landmark achievement has been driven by groundbreaking innovations from various research groups across the globe, heralding what experts hail as a “revolutionary” year that could significantly expedite the proliferation of solar energy.
As the quest for sustainable energy sources intensifies, conventional solar panels, reliant on silicon-based cells, have been inching towards the upper limit of their ability to convert sunlight into electricity, plateauing at around 29%. This coincides with a dire urgency to accelerate the deployment of solar power infrastructure by a factor of ten in order to effectively combat the escalating climate crisis, as asserted by the scientific community.
A pioneering advancement involves layering perovskite, an alternative semiconductor, atop the existing silicon layer in solar cells. This ingenious strategy captures blue light from the visible spectrum, complementing the silicon’s absorption of red light and ultimately enhancing the overall light capture efficiency. By augmenting energy absorption per cell, the cost of solar-generated electricity is further reduced, propelling the rapid expansion of deployment. This is a critical facet of mitigating global heating, ensuring a more sustainable future.
The perovskite-silicon hybrid cells, often referred to as “tandem” cells, have been under intensive research for nearly a decade. Recent strides in technical refinement have now propelled these cells beyond the significant 30% threshold.
“This year is a revolutionary year,” said Prof Stefaan De Wolf, at King Abdullah University of Science and Technology in Saudi Arabia. “It’s very exciting that things are moving rapidly with multiple groups.”
While initial research and development investments have been made, experts suggest that if the scaling-up of production for tandem cells progresses smoothly, commercial availability could be realised within approximately five years, a timeline that synchronises with the point at which silicon-only cells reach their maximum efficiency potential.
Two research groups have released detailed accounts of their efficiency breakthroughs in the journal Science, with at least two more known to have achieved efficiencies exceeding 30%. Presently, the efficiency record for silicon-only solar cells stands at 24.5% for commercial cells and 27% for laboratory cells, a value that is approaching the practical upper limit of 29%.
A research group led by Prof Steve Albrecht at the Helmholtz Center Berlin for Materials and Energy has notably documented achieving efficiencies of up to 32.5% for silicon-perovskite cells. Meanwhile, another team under the guidance of Dr Xin Yu Chin at the Federal Institute of Technology in Lausanne, Switzerland, demonstrated an efficiency of 31.25%. They have highlighted the tandem cells’ potential for both high efficiency and low manufacturing costs.
“What these two groups have shown are really milestones,” said De Wolf. His own group achieved 33.7% efficiency with a tandem cell in June, but has yet to publish the results in a journal. All the efficiency measurements were independently verified.
“Overcoming the 30% threshold provides confidence that high performance, low-cost PVs can be brought to the market,” said De Wolf. Global solar power capacity reached 1.2 terawatts (TW) in 2022. “Yet to avert the catastrophic scenarios associated with global warming, the total capacity needs to increase to about 75TW by 2050,” he said.
The solar industry is also part of the race to high efficiency. Chinese company LONGi, the world’s biggest producer of solar cells, announced in June they had reached 33.5% in their research. “Reducing the cost of electricity remains the perpetual theme driving the development of the photovoltaic industry,” said Li Zhenguo, the president of LONGi.
“The industry is running very, very fast,” De Wolf said. “And I’m sure that multiple companies are working on this in China.” Europe and the US need to increase its research and development funding to keep up, he said.
Notably, the realm of high-efficiency solar cells above the 30% benchmark is currently occupied by smaller prototypes, measuring a mere 1cm by 1cm. A critical phase ahead involves scaling these innovations to the dimensions of commercial cells, which typically measure 15cm squares or even larger.
Progress in this direction has already been initiated, with UK-based Oxford PV boasting a record-breaking 28.6% efficiency for a commercial-sized cell. “Solar is already one of the least expensive and cleanest forms of energy available, and our technology will make it even more affordable,” said Chris Case, chief technology officer at Oxford PV.
Importantly, this achievement was realised using the same production line already responsible for manufacturing tandem cells with 27% efficiency, signalling the potential for scaling up these high-efficiency variants.
While the upfront cost of tandem cells may exceed that of silicon-only counterparts, experts emphasise that the expense of the cells themselves constitutes only a fraction of the overall expenditure in producing and installing solar panels. However, a significant question looms: the long-term degradation rate of tandem cells under real-world conditions remains unresolved.
Currently, solar cells maintain 80-90% capacity even after 25 years of use. Matching or exceeding this stability threshold will be crucial for the successful integration of tandem cells into mainstream solar power infrastructure.
A pivotal factor in the impressive efficiencies achieved by the German and Swiss research groups was their approach to addressing minuscule defects on the surface of the perovskite layer. These defects hindered the flow of electrons, resulting in reduced efficiency.
A strategic solution emerged: the introduction of an organic molecular layer between the perovskite and the conducting layer through which electrical current flows. This intermediary layer effectively compensated for the defects, enhancing the overall efficiency of the cell.
What stands out is that different research groups have adopted distinct methods to tackle this challenge, offering a spectrum of options in the quest for the most effective and commercially viable design. “There’s still lots of room to go further,” he said. “I believe that the practical limit is well beyond 35%”, said De Wolf.
Prof Rob Gross, director of the UK Energy Research Centre, said: “Solar is already a low-cost way to generate electricity and has a wide resource base across the world. The cost reductions already achieved are the main reason solar now plays such a large role in scenarios of decarbonised energy systems. Improvements in efficiency have the potential to increase the output of solar and therefore will help to reinforce that effect.”
While other solar technologies, such as multi-junction cells boasting efficiency rates as high as 47%, exist, they remain prohibitively expensive for widespread use. These advanced solutions are confined to specialised applications, such as space satellites or situations where sunlight is intensely concentrated on the cells.
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