Electroluminescence in polymer-fullerene photovoltaic cells

We report electroluminescence (EL) in photovoltaic (PV) cells based on semiconducting poly mer-fullerene composites. By applying a forward bias to the PV cells, the devices exhibited a clear EL action with a peak around 1.5 eV. We ascribe this peak to an "electric field-assisted exciplex" formed between the electrons in the fullerenes and the holes in the polymers, thereby resulting in radiative recombination in the composites. This finding is totally unexpected because of a strong photoluminescence quenching in the same materials. Since the same devices also showed typical photovoltaic effects under illumination, our results demonstrate a dual functionality in one device; polymer photovoltaic cells and polymer light-emitting diodes. (c) 2005 American Institute of Physics.