S. Korean researchers set world record with perovskite tandem solar cell at 26.7% efficiency

A next-generation perovskite tandem solar cell developed by South Korean researchers has set a new world record.

The Korea Institute of Energy Research announced Tuesday that its Solar Energy Research Division achieved a certified world-record efficiency of 26.7 percent in the perovskite/CIGS tandem solar cell category.

The achievement was officially certified by Germany's Fraunhofer Institute for Solar Energy Systems, known as Fraunhofer ISE, and has been listed as the world's top record in the Best Research-Cell Efficiencies Chart published by the US National Renewable Energy Laboratory (NREL).

The record surpasses the 26.3 percent efficiency achieved last year by a joint research team from Seoul National University and the Korea Institute of Science and Technology, which had previously held the world record in the same category. The back-to-back breakthroughs, outpacing rivals in China and Germany, demonstrate South Korea's leading position in next-generation thin-film solar cell technology.

Solar power generation currently relies mainly on silicon-based single-junction solar cells, which are favored for their low production costs and suitability for mass production. Their power conversion efficiency has clear limits, however, driving the development of flexible thin-film perovskite/CIGS tandem solar cells that stack a perovskite cell on top of a CIGS cell to boost efficiency. CIGS-based thin-film solar cells are extremely lightweight and flexible, making them suitable for curved surfaces such as buildings, vehicles and aircraft. They have yet to reach commercialization, however, due to lower efficiency and greater manufacturing complexity compared with perovskite/silicon tandem cells.

The perovskite/CIGS tandem solar cell developed by the research team places a perovskite cell on top and a CIGS cell on the bottom, allowing the two layers to absorb sunlight across different wavelength ranges. Because both materials can be fabricated as thin films, the cell combines high efficiency with the advantages of being lightweight and flexible.

Combining the two cells into a single device poses challenges: the perovskite light-absorbing layer can degrade during integration, and certain component layers may absorb light unnecessarily, reducing performance. The research team analyzed the sources of these losses and developed interfacial layer materials and process technology to minimize damage to the perovskite layer. The team also optimized the structure of the upper transparent electrode and charge transport layer, successfully reducing unnecessary light absorption and minimizing photocurrent losses.

Through these improvements, the team achieved an efficiency of 27 percent under laboratory conditions and received a certified efficiency of 26.7 percent from Fraunhofer ISE.

The technology is expected to broaden the applications of solar power generation by producing more electricity from the same surface area. Its lightweight, flexible thin-film structure makes it well suited not only for buildings and vehicles but also for small satellites and space-based data centers — future space industry applications where weight and installation area are critical constraints.

"This achievement is significant because we simultaneously reduced both interfacial losses and optical losses that occur when combining perovskite and CIGS, improving efficiency and stability at the same time," said Jeong In-young, a senior researcher at the institute's Solar Energy Research Division. "Having our efficiency verified by a world-renowned certification body and listed as the top record is an objective recognition of the competitiveness of our technology," Jeong added.