Charge photogeneration and recombination in poly[2-methoxy-5-(2′-ethyl-hexoxy-p-phenylene vinylene]:fullerene composite films studied by photocurrent response

The\ua0photocurrent\ua0spectral responses\ua0of poly[2-methoxy-5-(2′-ethyl-hexoxy-p-phenylene vinylene]:fullerene (C60) composites are measured as a function of C60 concentration. At low concentration, the relationship between the external quantum efficiency (EQE) and\ua0absorption spectra\ua0is exhibited as the strengthened antibatic effect, and the EQE of the composite devices declines with increasing concentration of C60. At higher concentration, however, the maximum EQE gradually coincides with the absorption peak (symbatic response) and the EQE of composite devices begins to increase with increasing C60 concentration. It is proposed that at low concentration,\ua0dopant\ua0C60 increases the self-absorption rate of\ua0composite films, and charge trapping by C60 molecules causes the loss of efficiency. At high C60 concentration, the large-scale aggregations in composite films build pathways for charge carrier transport to respective\ua0electrodes, inhibiting the self-absorption effect and charge recombination on C60