Researchers from Germany’s Helmholtz-Zentrum Berlin (HZB) and Humboldt-Universität in Germany claim to have achieved a world record power conversion efficiency for a tandem solar cell based on a top perovskite device and a bottom cell based on copper, indium, gallium and selenium (CIGS).

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, noting that the result was already included in the Solar Cell Efficiency Tables.

The previous world record of 25.17% was achieved by Tokyo City University in Japan in mid-May. This result was verified by Japan’s National Institute of Advanced Industrial Science and Technology (AIST).

The German team explored CIGS-based bottom cells with carefully tuned band gaps of 1.05 eV and 1.1 eV, alongside the use of two different thicknesses of aluminium-doped zinc oxide layers with otherwise comparable characteristics. In parallel, it expanded the device design space by testing multiple cell architectures, building directly on the continuous performance gains achieved in their previous record-setting work.

The academics systematically screened combinations of nickel oxide (NiOx) and self-assembled monolayers (SAMs) as hole transport layers, seeking interface configurations that could simultaneously improve charge selectivity and suppress recombination pathways. Moreover, they refined the contact formation by precisely controlling the initial thermal evaporation rate of buckminsterfullerene (C60) deposited onto an ultra-thin 1 nm lithium fluoride (LiF) passivation layer, enabling what they defined as a more controlled interface formation and improved electronic alignment.

Utilizing the proposed cell configurations, the scientists also fabricated a 2.25 cm² module reaching an efficiency of approximately 19.7%, claiming that the optimized interface and contact strategy could translate beyond the lab-scale device into a more integrated architecture.

No more technical details about the cell technology were provided.