The Commercialization Race for Tandem Solar Cells Intensifies: Distinctive Technological Strategies of Korea, China, and Japan and the Breakthrough of 34.76% Efficiency
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As the global solar industry focuses on tandem solar cells as the next-generation technology to surpass the physical limits of silicon single cells, leading companies from Korea, China, and Japan are fiercely competing to capture the market with different approaches. According to the latest technology trends revealed at the ‘Tandem PV Special Forum’ held at the Daejeon Convention Center on December 2, 2025, there is a consensus in the industry that tandem technology is becoming the next-generation standard, as silicon single-cell efficiency nears its theoretical limit of 29%.
The most noteworthy achievement is the world-record efficiency of 34.76% achieved by China’s Jinko Solar, based in Shanghai. This is significant not only because it was achieved at the industrial level based on TOPCon, but also because it highlights the advantage of China’s large-scale manufacturing infrastructure. Menglei Xu, Director at Jinko Solar, emphasized that “the commercialization potential of tandem technology is determined by the hundreds of gigawatts of existing TOPCon production facilities,” showcasing China’s manufacturing prowess. Currently, out of the global solar manufacturing capacity of 1.3 terawatts (TW), 1.1 TW is based on TOPCon technology, demonstrating the practicality of China’s strategy.
In contrast, Korea’s HD Hyundai Energy Solutions, based in Ulsan, is proposing a realistic industrialization path based on heterojunction (HJT). Chief Research Engineer Kim Sang-ho explained, “The actual industrialization of tandem technology depends on the stability of the top cell, process scalability, and the ease of conversion of the bottom cell,” and stated that “HJT is currently the most realistic candidate for the bottom cell.” HJT has the advantage of transitioning to tandem without significantly altering existing production infrastructure due to its low-temperature process and simple structure. HD Hyundai Energy Solutions has established a pilot production line through a government project and achieved 18.7% efficiency by applying a vacuum-deposited top layer on HJT, which is significant as it was obtained under conditions similar to actual production processes.
Distinctive Strategies and Industrialization Approaches by Technology
Analyzing the technological strategies of companies from each country reveals clear differentiation. Kim Ki-hong, Tandem Commercialization Executive at Hanwha Solutions, based in Seoul, Korea, presented an approach emphasizing compatibility with existing facilities and ease of operation. Hanwha is particularly focused on standardizing ‘low-temperature lamination’ technology to protect heat-sensitive perovskite materials while suppressing cost increases from additional process steps. This approach is based on the belief that only when high-efficiency silicon cells secure bifacial efficiency at the HJT level can the high-efficiency advantage of tandem be fully realized.
China’s LONGi Green Energy, based in Xi’an, is pursuing a more aggressive strategy. Liang Fang, Director of LONGi’s Second Research Institute, proposed a super-gap strategy that adopts ‘back contact (BC)’ technology, which seeks extreme efficiency despite high process complexity, for the bottom cell. LONGi is developing technology to precisely control the crystallization of microcrystalline materials by raising the tip temperature to 1000 degrees through laser processing, as part of efforts to overcome the current matching constraints of the mainstream two-terminal electrode connection method.
Innovation to secure cost competitiveness is also actively underway. Wang Wei, CTO of SPIC New Energy, suggested the possibility of securing price competitiveness for HJT through the introduction of copper plating technology. “In 2022, we established a pure copper plating line with a capacity of 300MW, drastically reducing silver usage from 20mg per watt to less than 5mg,” he said, “thereby reducing manufacturing costs by 0.03 yuan per meter and ensuring product reliability by combining with low-temperature processes.” Additionally, HJT can use thin wafers at the 100-micrometer (μm) level, offering significant cost reduction potential compared to TOPCon (130μm).
Technical Limitations and Commercialization Challenges
Stefan Glunz, Head of the Solar Department at Germany’s Fraunhofer ISE, pointed out the inherent challenges of tandem technology. He warned against excessive expectations, stating, “While the industry often expects efficiencies in the 40% range for tandem, a realistic target is 39% when fundamental defects are considered.” He also noted that the spin-coating method commonly used in laboratories is “not suitable for mass production processes because it is difficult to uniformly coat large-area substrates and expand to industrial equipment,” emphasizing the need for a transition to large-area, deposition-based processes.
There is also an analysis that improving interface quality is key to the success of tandem technology. Glunz explained, “A good solar cell ultimately depends on interface quality,” and noted that “surface and interface treatment effects determine performance in both silicon and perovskite.” While there has been significant progress in reducing optical losses, electrical losses still limit the power generation potential of silicon cells. To address this, Fraunhofer ISE has begun demonstrations to ensure uniform coating and quality reproducibility by establishing 600mm-class hybrid deposition equipment.
Technical challenges at the module stage are also significant. Lamination temperature was mentioned as a representative constraint, with experimental results showing that perovskite is damaged and cannot be encapsulated at around 100°C, but stability is secured at around 140°C. This suggests that the choice of encapsulation materials and process conditions will be key variables in the commercialization of tandem modules.
International collaborative research in Europe is also showing notable results. The ‘Horizon Europe SolMates’ project, involving 14 institutions from 18 countries, achieved 26.8% efficiency in laboratory standards and 24.6% efficiency in certified measurements by combining CIGS bottom cells with perovskite top cells. Nikolaus Weinberger, a professor at the University of Innsbruck in Austria, emphasized, “In addition to efficiency improvement, data sharing, recycling, and carbon reduction are the core goals of SolMates,” demonstrating Europe’s approach focused on sustainability.
Market conditions are also impacting technological advancements. Chris Case, Chief Scientist at Oxford PV, noted, “The current global solar manufacturing capacity is 1.3 terawatts (TW), with 1.1 TW being TOPCon. This is nearly double the actual demand,” highlighting the severe oversupply issue. However, he emphasized, “With demand expected to reach 2-3 TW by 2030, growth is essential in the long term,” and stated, “It is now necessary to shift from a simple watt (W) competition to a kilowatt-hour (kWh) sales strategy that provides more energy to customers.”
Regional market characteristics are also influencing technology choices. Cosimo Gerardi, CTO of 3SUN-ENEL, analyzed, “While TOPCon is dominant in China, the situation is different in the US and Europe,” noting that “the possibility of TOPCon patent disputes in the US and high electricity prices provide a niche for high-efficiency technologies like HJT.” This shows that technological advancement is not determined solely by efficiency or cost but must consider geopolitical factors and regional market characteristics comprehensively.
The commercialization of tandem solar cell technology is now moving beyond the laboratory to the verification stage in actual industrial settings. The differentiated strategies based on existing infrastructure, manufacturing capabilities, and market accessibility of companies from each country are expected to determine the future market landscape. The outcome of China’s large-scale TOPCon-based advantage, Korea’s realistic HJT-based approach, and Europe’s sustainability-focused innovation is being closely watched. Particularly, companies that simultaneously solve the three major challenges of achieving the realistic efficiency target of 39%, stabilizing large-area processes, and securing cost competitiveness are expected to lead the next-generation solar market.
This article was written with reference to the following sources:
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