Cascade organic solar cells with energy-level-matched three photon-harvesting layers

The performances of organic photovoltaic cells were improved by matching the energy levels of three photon-harvesting layers with distinct light absorption spectra. Pentacene, phthalocyanine, and C70, which have shallow, intermediate, and deep energy levels, respectively, were introduced as photon harvesting layers to form a cascade structure and secure appropriate band offsets at all interfaces. This architecture yielded higher values of the open-circuit voltage and short-circuit current density than a standard bilayer structure based on pentacene and C70. A device prepared with metal-free phthalocyanine performed better than a device with Cu phthalocyanine because the energy levels were more appropriately tuned.