Highly efficient (11.1%) small molecule multi-junction organic photovoltaic cells

We present multi-junction small molecule organic photovoltaic (OPV) cells with efficiencies over 11%. The devices consist of two or three, vacuum thermally evaporated planar-mixed heterojunction sub-cells with minimal absorption overlap between the cells. By introducing a transparent interconnecting layer, a dual element (tandem) cell achieves a power conversion efficiency of 10.0 ± 0.5%. We further improve the cell performance by adding an additional (3^rd) sub-cell that absorbs at the second order optical interference maximum within the stack. The triple-junction cell significantly improves the quantum efficiency at shorter wavelengths, achieving a power conversion efficiency of 11.1 ± 0.5%, which to our knowledge, is the highest reported for a multi-junction OPV cell in the scientific literature.