Electronic Structure of C(60)/Zinc Phthalocyanine/V(2)O(5) Interfaces Studied Using Photoemission Spectroscopy for Organic Photovoltaic Applications

The interfacial electronic structures of a bilayer of fullerene (C(60)) and zinc phthalocyanine (ZnPc) grown on vanadium pentoxide (V(2)O(5)) thin films deposited using radio frequency sputtering under various conditions were studied using X-ray and ultraviolet photoelectron spectroscopy. The energy difference between the highest occupied molecular orbital (HOMO) level of the ZnPc layer and the lowest unoccupied molecular orbital (LUMO) level of the C(60) layer was determined and compared with that grown on an indium tin oxide (ITO) substrate. The energy difference of a heterojunction on all V(2)O(5) was found to be 1.3~1.4 eV, while that on ITO was 1.1 eV. This difference could be due to the higher binding energy of the HOMO of ZnPc on V(2)O(5) than that on ITO regardless of work functions of the substrates. We also determined the complete energy level diagrams of C(60)/ZnPc on V(2)O(5) and ITO.