Interfacial electronic structure of C60/ZnPc/AZO on photoemission spectroscopy for organic photovoltaic applications

- The electronic structure of a bilayer on AZO has been evaluated by UPS and XPS.
- The energy difference between the ZnPc HOMO and the C60 LUMO was determined.
- The result is discussed in terms of the work function and resistivity of each TCO.

The interfacial electronic structure of a bilayer of fullerene (C60) and zinc phthalocyanine (ZnPc) grown on aluminum-doped zinc oxide (AZO) substrates has been evaluated by X-ray and ultraviolet photoemission 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 C60 layer (EDHOMO − EALUMO) was determined and compared to that grown on an indium tin oxide (ITO) substrate. The EDHOMO − EALUMO value of the heterojunction on AZO was 1.4 eV, while that on ITO was 1.1 eV. This result is discussed in terms of the differences of the work function and resistivity of each transparent conductive oxide. We also obtained complete energy level diagrams of C60/ZnPc/AZO and C60/ZnPc/ITO.