Conjugated polymer/nanostructured oxide semiconductor composite photovoltaic devices

Organic semiconductor-based photovoltaic devices offer the promise of low cost photovoltaic technology that can be manufactured via large-scale, roll-to-roll printing techniques. Existing organic photovoltaic devices are currently limited to solar power conversion efficiencies of 3-5%. The reasons for this include poor overlap between the absorption spectrum of the organic chromophores and the solar spectrum, non-ideal band alignment between the donor and acceptor species, and low charge carrier mobilities resulting from the disordered nature of organic semiconductors. To address the latter issues, we are investigating the development of nanostructured oxide / conjugated polymer composite photovoltaic (PV) devices. These composites can take advantage of the high electron mobilities attainable in oxide semiconductors and can be fabricated using low-temperature solution-based growth techniques. Additionally, the morphology of the composite can be controlled in a systematic way through control of the nanostructured oxide growth. For both ZnO and TiO₂, nanostructures that are vertically aligned with respect to the substrate can be grown. Here we discuss the fabrication of such nanostructures and present preliminary results from ZnO nanocarpet/poly(3-hexylthiophene) composite PV devices.