Utilizing n-type vanadium oxide films as hole-extracting layers for small molecule organic photovoltaics

We report increased cell performance for boron subphthalocyanine chloride (SubPc)/fullerene (C60) organic photovoltaic (OPV) cells when thermally evaporated vanadium oxide (V2OX) thin films are incorporated as a hole-extracting layer at the indium-tin oxide (ITO)/SubPc interface. Ultra-violet photoemission spectroscopy (UPS) studies of the V2OX films reveal highly n-type character, with a large work function of 6.8 eV. This correlates well with recently reported data for other metal oxide hole-extracting layers, such as molybdenum oxide and tungsten oxide, in contrast to the p-type character previously reported for V2OX films. There is significant improvement in energy level alignment for hole-extraction when cells utilise the V2OX layer at the ITO/SubPc interface, resulting in substantial increases in open circuit voltage (VOC) and power conversion efficiency (ηp).