Dynamics of photoexcited carriers in poly(p-phenylene vinylene) and its soluble derivative

Summary form only given. We report the results of comprehensive measurements of photoconductivity (PC) in films of poly(p phenylenevinylene), PPV and its soluble derivative, poly[2-methoxy, 5-(2´-ethyl-hexyloxy)-p phenylenevinylene], MEH-PPV. The initial fast transient photocurrent decays exponentially in the subnanosecond time regime, followed by a thermally-activated weak slower component. The magnitude of the peak transient photocurrent is proportional to the light intensity and the electric field, and independent of temperature. The transient PC of MEH-PPV is smaller than that of PPV by a factor of 10. Since the interchain coupling in MEH-PPV is weaker than in PPV, (due to the large side groups), interchain transport is inhibited. As a result, the early-time recombination is enhanced. Measurements of the spectral response of both transient and steady-state PC demonstrate that the onset of the PC coincides with that of photo-absorption, consistent with the photogeneration of charge carriers via an interband transition.