Interfacial electronic structures in an organic double-heterostructure photovoltaic cell

The electronic structure of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline/fullerene/ copper-phthalocyanine double heterostructure in a typical organic photovoltaic cell was studied by photoemission spectroscopy. The results show that the traditional vacuum energy level lineup is not valid for these organic heterojunctions, which suggests formation of interface dipole and energy level bending across the interface due to charge transfer. Based on the measured energy levels using x-ray and ultraviolet photoemission spectroscopies, important parameters such as the theoretical maximum of the open circuit voltage are extracted, and their impacts on charge photogeneration process are discussed. (c) 2008 American Institute of Physics.