Subnanosecond transient photoconductivity in poly(3-hexylthiophene)

Abstract

We present the results of comprehensive measurements of photoconductivity in films of poly(3-hexylthiophene-2,5-yl), a soluble alkyl derivative of polythiophene. Transient measurements in the subnanosecond-time regime reveal a fast, temperature-independent photoconductive response which decays within about 100 ps after photoexcitation. Information on the anisotropy of the transient photocurrent is obtained from nonoriented films by using polarized light and varying the direction of the polarization with respect to the biasing electric field; the results imply that intrachain photoexcitation of polarons is the dominant process. Measurements of the spectral response of both transient and steady-state photoconductivity demonstrate that the magnitude of the photocurrent follows the absorption profile, consistent with the photogeneration of free carriers via an interband transition in a system with relatively weak effective electron-electron interactions.