Photoelectrochemical response and photoconductivity of poly(3-methylthiophene)

We report on the photoelectrochemical response and photoconductivity of pol y(3-methylthiophene), PMeT, films deposited on different substrates. The fr equency dependency of the modulated photoconductivity of PMeT (rho = 3.6 x 10(3) Omega cm) is sublinear indicating that the measured photoconductivity is not due to a thermal effect caused by sample heating. An interesting fe ature was the larger backwall photoconductivity (with the laser beam reachi ng the film from the substrate side), when compared to photoconductivity in the normal, frontwall illumination. This result is an indication for heter ogeneity in the deposited film. The photoelectrochemical response of PMeT f ilms in contact with the electrolyte was studied by spectral response and b y the time dependence of the photoelectrochemical response under irradiatio n with the Ar+ laser light (close to the maximum of the spectral photorespo nse), with light intensity varying from 10(-5) W cm(-2) to 30 mW cm(-2). Fr om that experiment we can infer that charge trapping occurs mainly in the p olymer surface in contact with the electrolyte. Another experiment was perf ormed with two different light beams, one from a lamp plus monochromator, c hopped and at low intensity and another from an Ar+ laser, continuous and a t high intensity. When the laser beam incides from the electrolyte side, i. e. when light is absorbed in the space-charge layer, we observe a strong dr op in the photocurrent. We suppose that the same space-charge layer trappin g phenomenon is responsible for the drop in the photocurrent. (C) 1998 Else vier Science Ltd. All rights reserved.