Interfacial electronic structures of C60 molecules on a K-doped CuPc surface

The evolution of interfacial electronic structures of C-60 on a K-doped CuPc surface is studied via synchrotron-radiation photoemission spectroscopy. Layer-by-layer growth has been identified. As the heterointerface formed, the K diffuses into the C-60 overlayer, and transfers negative charge into the lowest unoccupied molecular orbital (LUMO) of C-60, resulting in a significant interfacial dipole potential. With K doping, increased photon absorption, due to the existence of gap states, and an enhanced energy-level difference between the LUMO of C-60 and the highest occupied molecular orbital of CuPc could possibly improve the efficiency of organic photovoltaic devices.