Improved efficiency of zinc phthalocyanine/C60 based photovoltaic cells via nanoscale interface modification

The photovoltaic performance of zinc phthalocyanine (ZnPc)/C-60 heterojunctions is improved by alternately depositing ultrathin active layers between the two bulk layers. Using a proper multilayer structure, a 60% improvement in conversion efficiency under AM1.5 illumination is obtained, in comparison with that of flat heterojunctions. Transmission electron microscope investigations reveal an effective phase separation of ZnPc and C-60 and a high degree of crystalline ordering of C-60 in this system. The authors propose that an interpenetrating interface is formed, which facilitates both exciton separation and charge transport, and enhances the photocurrent from ZnPc due to an extended photoactive region. (C) 2007 American Institute of Physics.