Electronic properties and open-circuit voltage enhancement in mixed copper phthalocyanine: Fullerene bulk heterojunction photovoltaic devices

While bulk heterojunctions (HJ) have been used in organic photovoltaic (OPV) devices, there are few studies on their interface electronics and mechanisms on device performance. Here, we studied the electronic structure of a mixed CuPc: C₆₀ and a discrete CuPc/ C₆₀ junctions using photoemission spectroscopy. The HOMO_CuPc -LUMO_C60 energy offset, which controls the theoretical maximum open-circuit voltage (Voc), was increased from 0.64 to 1.13 eV by mixing CuPc with C₆₀. This V _oc increase is attributed to the underlying substrate work function and charge transfer between two molecules. The results provide an understanding of the V_oc enhancement in OPV devices with bulk HJ. © 2009 American Institute of Physics.