Soft X-ray Spectroscopy of C60/Copper Phthalocyanine/MoO3 Interfaces: Role of Reduced MoO3 on Energetic Band Alignment and Improved Performance

The interfacial electronic structure of C-60/copper phthalocyanine (CuPc)/molybdenum trioxide (MoO3) thin films grown in situ on indium tin oxide (ITO) substrates has been studied using synchrotron radiation-excited photoelectron spectroscopy in an attempt to understand the influence of oxide interlayers on the performance of small molecule organic photovoltaic devices. The MoO3 layer on ITO is found to significantly increase the work function of the substrate and induces large interface dipoles and band bending at the CuPc/MoO3 interface. The large band bending confirms the formation of an internal potential that assists hole extraction from the CuPc layer to the electrode. The electronic structure of the MoO3 layer on ITO was also examined using various soft X-ray spectroscopies to probe the conductive nature of the MoO3 thin film.