Advanced cells exceed the constraints of current cells, paving the way for more affordable and efficient solar energy deployment.
Solar energy cells have now exceeded the significant benchmark of 30% energy conversion efficiency, thanks to the collaborative efforts of various global research teams. This achievement marks a transformative year in the field, as one specialist noted, and could hasten the expansion of solar energy.
Present-day solar panels, which utilize silicon-based cells, are quickly nearing their peak sunlight-to-electricity conversion rate of 29%. Concurrently, scientists assert that the installation of solar power must multiply by ten to effectively combat climate change.
The innovation lies in the addition of a perovskite layer, a different semiconductor, atop the silicon layer. This combination captures both blue and red light from the visible spectrum, enhancing the overall light absorption. Consequently, solar electricity becomes even more cost-effective, and its deployment can be expedited to mitigate global warming.
The combined perovskite-silicon “tandem” cells have been a subject of study for nearly ten years, but recent advancements have propelled them beyond the 30% efficiency mark. Experts predict that, with smooth scaling-up of production, these tandem cells could reach the market within five years, coinciding with the time silicon-only cells achieve their maximum efficiency.
Two research groups disclosed their efficiency breakthroughs in the Science journal last Thursday, and at least two more are known to have exceeded 30%.
“This is a groundbreaking year,” proclaimed Prof Stefaan De Wolf, at King Abdullah University of Science and Technology in Saudi Arabia. “The rapid progress across multiple teams is truly exhilarating.”
The existing efficiency record for silicon-only solar cells stands at 24.5% for commercial cells and 27% in laboratory settings. The latter might be nearing the practical limit of 29%.
However, one team, headed by Prof Steve Albrecht at the Helmholtz Center Berlin for Materials and Energy in Germany, has revealed their achievement of up to 32.5% efficiency with silicon-perovskite cells. Another team, led by Dr. Xin Yu Chin at the Federal Institute of Technology in Lausanne, Switzerland, showcased an efficiency of 31.25%, emphasizing the tandem cells’ “capacity for both superior efficiency and reduced production costs.”
“These milestones demonstrated by the two groups are truly significant,” De Wolf remarked. His team reached 33.7% efficiency with a tandem cell in June but has not yet published the findings in a scientific journal. All efficiency assessments were independently confirmed.
“Breaking the 30% barrier instills confidence that high-quality, affordable photovoltaics can enter the market,” De Wolf stated. Global solar power capacity hit 1.2 terawatts (TW) in 2022. “To prevent the disastrous consequences of global warming, the total capacity must rise to approximately 75TW by 2050,” he added.
The solar industry is also engaged in the pursuit of higher efficiency. LONGi, the world’s largest solar cell manufacturer based in China, announced in June that they had achieved 33.5% efficiency in their research. “The ongoing reduction of electricity costs is the constant motivation behind the evolution of the photovoltaic industry,” said Li Zhenguo, LONGi’s president.
“The industry is advancing at an incredible pace,” De Wolf observed. “I’m confident that numerous companies in China are focusing on this.” He also emphasized that Europe and the US must boost research and development funding to keep pace and contribute to the accelerated deployment of solar energy.
Currently, all high-efficiency tandem cells exceeding 30% efficiency are small, measuring only 1cm by 1cm. They must now be enlarged to commercial cell dimensions, typically 15cm squares or more.
The scaling process is already in motion, with UK-based Oxford PV announcing a record 28.6% efficiency for a commercial-sized cell in May. “Solar energy is already among the cleanest and most affordable energy sources, and our technology will make it even more accessible,” stated Chris Case, Oxford PV’s chief technology officer.
The Oxford PV cell was manufactured on the same production line already used for commercial-sized tandem cells with 27% efficiency, now being produced in growing quantities. While tandem cells might be pricier than silicon-only cells, they constitute only a minor portion of the overall cost of producing and installing solar panels, according to De Wolf.
A remaining challenge is determining the rate at which tandem cells degrade in real-world scenarios. Current solar cells retain 80-90% of their capacity after 25 years, and De Wolf believes tandems must meet this standard, though data on their stability is still limited.
The key to the German and Swiss groups’ higher efficiencies was addressing minuscule defects on the perovskite layer’s surface. These defects allowed some electrons activated by solar photons to reenter the perovskite, reducing the cell’s efficiency.
The remedy involved placing a layer of organic molecules between the perovskite and the conducting layer, compensating for the defects.
Notably, all the groups employed diverse methods to tackle the issue, providing more alternatives in the quest for the optimal commercial design, De Wolf noted. “There’s still substantial potential for further advancement,” he said. “I’m convinced that the practical limit is far above 35%.”
Prof Rob Gross, director of the UK Energy Research Centre, commented: “Solar energy is already an economical means of electricity generation with a vast global resource base. The cost reductions already realized are the primary reason solar energy now plays a significant role in decarbonized energy system scenarios. Efficiency enhancements have the potential to boost solar output, thereby reinforcing this trend.”
Other technologies, like multi-junction cells, can achieve efficiencies as high as 47%, but their high production costs render them suitable only for specialized applications, such as space satellites or highly concentrated sunlight exposure.
