An HZB team has fabricated and characterised a thin-film tandem solar cell made of perovskite and CIGSe. They relied on a simple, robust fabrication process that is also suitable for scaling up to large surface areas. The tandem solar cell is a fully thin film device with an impressive efficiency of 21.6 %. With further improvements it might reach efficiencies above 30 %.
Tandem solar cells consist of two semiconductors with different band gaps, enabling them to use a larger fraction of the solar spectrum for generating electricity. This concept is particularly successful when conventional absorber layers such as silicon or copper indium gallium selenide (CIGSe) are combined with the new metal-halide semiconductor perovskite. This is because perovskites convert the blue, high-energy portions of sunlight into electrical energy very efficiently, while silicon or CIGSe convert the red and near-infrared portions effectively.