The electronic structure of C60/ZnPc interface for organic photovoltaic device with blended layer architecture

The interfacial electronic structures of fullerene (C-60)/zinc-phthalocyanine (ZnPc) and C-60/ZnPc:C-60 (50 wt %) containing a blended layer were investigated by in situ ultraviolet photoelectron spectroscopy (UPS), in an attempt to understand the role of the blended layer in improving the performance of organic photovoltaic devices that contain such layers. From the UPS spectra, the band bending found to be 0.30 eV in the ZnPc layer and 0.43 eV in the C-60 layer at the C-60/ZnPc interface. On the other hand, the band bending was 0.25 eV in both of the organic layers at the ZnPc:C-60/ZnPc interface and no significant band bending in the C-60 layer at the C-60/ZnPc:C-60 interface was found. The observed interface dipole was 0.06 eV at the C-60/ZnPc interface and 0.26 eV at the ZnPc:C-60/ZnPc interface. The offset between the highest unoccupied molecular orbital of ZnPc and the lowest occupied molecular orbital of C-60 was 0.75 eV at C-60/ZnPc and was 1.04 eV at the ZnPc:C-60/ZnPc interface. The increased offset can be attributed to an increase in the interface dipole, caused by the blending donor and acceptor material. The blending facilitates charge transfer between the donor and acceptor, resulting in an increase in the interface dipole, resulting in a larger offset.