Researchers at Tokyo City University in Japan have reportedly achieved a new world record power conversion efficiency for a tandem solar cell that combines a perovskite top cell with a copper-indium-gallium-selenide (CIGS) bottom cell. The two-terminal device has an active area of 1 cm² and reached a certified efficiency of 25.14%, with the result independently confirmed by Japan’s National Institute of Advanced Industrial Science and Technology (AIST).
This surpasses the previous record of 24.6% for a perovskite-CIGS tandem, which was set by Germany’s Helmholtz-Zentrum Berlin (HZB) in February 2025, after which groups worldwide had been trying to push the technology beyond the 25% threshold. The Japanese team notes that, until now, this 25% mark had remained out of reach despite intensive international research efforts.
The new record cell is built on a CIGS bottom device originally developed at AIST, paired with a perovskite top cell that uses an improved absorber layer with higher crystallinity. This enhancement is enabled by a newly introduced interfacial barrier layer between the two subcells, which provides a more favorable surface for perovskite growth, suppresses interfacial recombination losses, and blocks undesirable chemical reactions between the CIGS absorber and the perovskite precursor materials.
In the top perovskite cell, the researchers employed an indium tin oxide (ITO) substrate, a MeO-2PACz self-assembled monolayer (SAM), the perovskite absorber, and an electron transport stack consisting of buckminsterfullerene (C60) and an atomic-layer-deposited tin dioxide (ALD-SnO₂) layer, followed by an additional ITO layer, a magnesium fluoride (MgF₂) antireflection coating, and a silver contact. The CIGS bottom cell uses soda-lime glass (SLG) as the substrate, a molybdenum (Mo) back contact, the CIGS absorber layer, a cadmium sulfide (CdS) buffer, and a zinc oxide (ZnO) window layer.
Under standard test conditions, the tandem device delivered not only 25.14% efficiency but also an open-circuit voltage of 1.845 V, a short-circuit current density of 16.25 mA/cm², and a fill factor of 83.5%.
The team expects that further gains are possible by refining the device architecture to increase the short-circuit current, and they plan to speed up development toward practical applications through improved additives and passivation strategies, although detailed information on these aspects has not yet been disclosed.
