Sensitization of the photoconductivity of conducting polymers by C60: Photoinduced electron transfer.

Abstract

We have investigated the effect of photoinduced electron transfer on the photoconductivity (PC) of conducting polymer-${\mathrm{C}}_{60}$ films by comparing the photoconductivity (carrier generation and carrier transport) of the conducting polymer sensitized with ${\mathrm{C}}_{60}$ with that of the conducting polymer alone. We present time-resolved transient PC results, subnanosecond to 0.5 \ensuremath{\mu}s, obtained from poly[2-methoxy,5-(2'-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) and poly(3-octylthiophene) (P3OT), and from conducting polymer films sensitized with several concentrations of ${\mathrm{C}}_{60}$. Both the magnitude and the lifetime of the transient PC increase substantially on increasing the concentration of ${\mathrm{C}}_{60}$. The results imply that quantum efficiency for photogeneration of charge carriers is increased by photoinduced electron transfer and that early time recombination is inhibited by the spatial separation of the electron and hole on the ${\mathrm{C}}_{60}$ and the conducting polymer, respectively. The greater enhancement of the transient PC in MEH-PPV (nearly two orders of magnitude with the addition of a few percent of ${\mathrm{C}}_{60}$) than in P3OT (nearly one order of magnitude with the addition of a comparable amount of ${\mathrm{C}}_{60}$) suggests a higher probability of early time recombination in pristine MEH-PPV. As a result of the enhancement in the photogeneration efficiency and the carrier lifetime, the spectral response of the steady-state PC in both MEH-PPV/${\mathrm{C}}_{60}$ and P3OT/${\mathrm{C}}_{60}$ films is significantly enhanced throughout the entire spectral range from the near infrared to the ultraviolet.