Researchers from Humboldt University of Berlin (HU) and the Helmholtz-Zentrum Berlin (HZB) have set a new efficiency record of 25.5% for a tandem solar cell combining CIGSe (copper indium gallium selenide) with perovskite. The device, slightly larger than 1 cm², surpasses the team’s previous record of 24.6% achieved last year for the same material system.
The new result has been independently certified by the Fraunhofer Institute for Solar Energy Systems (ISE) and has been included in the widely recognized Solar Cell Efficiency Tables, often referred to as the “Green Tables,” which serve as a global benchmark for photovoltaic performance.
To achieve this improvement, the researchers optimized the tandem architecture by using CIGSe bottom cells with different band gaps and incorporating two thicknesses of aluminum-doped zinc oxide layers. Various device architectures were also explored, building on prior advances.
Further performance gains were enabled by interface engineering. Wuai Zhang, a Master’s student at HU and member of the Centre for the Science of Materials Berlin (CSMB), investigated combinations of nickel oxide and self-assembled monolayers (SAMs) to reduce interfacial losses and enhance device stability. Zhang also optimized the electron-selective contact, improving charge transport within the cell.
The work highlights the strength of collaboration within Berlin’s Adlershof research campus. “This record demonstrates how well collaboration in Adlershof works across laboratory boundaries,” said Prof. Emil List-Kratochvil, head of the Hybrid Devices group at HU.
