Korean researchers achieve world-record 26.7% efficiency for sub-1 cm² perovskite-CIGS tandem solar cell

Scientists at the Korea Institute of Energy Research (KIER) claim to have achieved a world-record power conversion efficiency of 26.7% for a tandem solar cell based on a perovskite top cell and a copper indium gallium selenide (CIGS) bottom cell.

They said the result was confirmed by Germany’s Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) and included in the Best Research-Cell Efficiency Chart maintained by the US Department of Energy’s National Laboratory of the Rookies.

The record applies to perovskite-CIGS tandem solar cells with an area of less than 1 cm².

The KIER researchers said both absorber materials used in the tandem device can be fabricated as thin films, offering the potential to combine high efficiency with a lightweight, flexible form factor.

“However, integrating the two solar cells can degrade the perovskite light-absorbing layer, while certain constituent layers may unnecessarily absorb light, thereby reducing overall performance,” they said. “We analyzed the various sources of these losses and developed interface materials and processing techniques to minimize damage to the perovskite layer. We also optimized the structures of the top transparent electrode and charge transport layer, reducing parasitic light absorption and minimizing photocurrent loss.”

The research group also said the cell achieved a laboratory-measured efficiency of 27%, without providing further details.

“This achievement is significant because it simultaneously improves efficiency and stability by mitigating both interfacial and optical losses that occur when integrating perovskite and CIGS solar cells,” said lead researcher In-Young Jeong. “Having our efficiency verified by a globally recognized certification body and recognized as a record-high value provides objective validation of the competitiveness of this technology.”

The previous world record for a perovskite-CIGS tandem cell in this size category was 26.3%, achieved by South Korea’s Korea Institute of Science and Technology (KIST) in July 2025.

For perovskite-CIGS tandem cells with an area exceeding 1 cm², the current world-record efficiency stands at 25.5%. The record is held by Germany’s Helmholtz-Zentrum Berlin (HZB) and Humboldt-Universität. The result was confirmed by the European Solar Test Installation (ESTI).

“The physics underlying our current cell architecture indicates that 25.5% is only an initial milestone, as in-house testing of similar designs has already achieved efficiencies of up to 27.5%,” HZB researcher Farias Basulto told pv magazine at the time, noting that the result was included in the Solar Cell Efficiency Tables.