Investigation of polybithiophene/n-TiO2 bilayers by electrochemical impedance spectroscopy and photoelectrochemistry

Extremely adhesive polybithiophene (PBT) films were grown on TiO2 in a new, two-step procedure using a silyl substituted thiophene derivative as a sur face coupling agent and a subsequent chemical polymerization process. Elect rochemical impedance and photocurrent measurements were carried out in orde r to achieve information on the semiconducting properties of both materials . When a PET film deposited onto TiO2 is reduced it can be described as a p -type semiconductor with a flatband potential of about 0.65 V (vs. SCE), wh ereas the n-type semiconductor TiO2 gives a flatband potential of about - 0 .4 V (vs. SCE). The photocurrent measurements show an anodic photocurrent a t wavelength of between 300 and 400 nm and a cathodic photocurrent of betwe en 400 and 600-700 nm, confirming the impedance measurements. The results o f the impedance and photocurrent measurements are summarized in a band stru cture model which explains the behaviour of the semiconductor electrode Ti/ n-TiO2/p-PBT. (C) 2001 Elsevier Science Ltd. All rights reserved.