Fullerene / SnO2-x interconnection layers for perovskite-perovskite tandem solar cells are shown to improve power conversion efficiency while simplifying device fabrication. These interconnection layers obviate the need for sputtered ITO layers, and they form Ohmic contact with both the narrow band gap and wide band gap sub-cells of the tandem devices. This invention challenges previous design rules for interconnection layers, demonstrating here that use of a heavily doped layer and slightly doped layer form effective interconnects, regardless of doping type.
· Power conversion efficiencies of 22.9% observed for resulting perovskite-perovskite tandem cells
· Avoids need for sputtering ITO which can damage the active perovskite layers
· SnO2-x layer protects wide band gap subcell from the spin coating of subsequent layers, including the narrow band gap perovskite layer.