Effect of white light irradiation on the systems ITO/poly(4,4 '-dipentoxy-2,2 ' bithiophene)/aluminium and ITO/poly(3-butylthiophene)/aluminium

The electrical characteristics of Al/poly(4,4'-dipentoxy-2,2'bithiophene)/I TO and of Al/poly(3-butylthiophene)/ITO Schottky diodes were investigated i n the dark and under white light illumination, In both cases a battery was found superimposed to the rectifying junctions, leading to a negative curre nt for positive bias applied in the dark. Under illumination, the build-up of a photoelectrochemical cell was demonstrated, which prevents the photovo ltaic parameters inherent to the Schottky junctions being observed. In the case of the Al/poly(4,4'-dipentoxy-2,2 'bithiophene)/ITO system a dependenc e of the photocurrent on the relative environmental humidity was revealed. All these findings were explained on the basis of the ion conductivity indu ced by the water absorbed by the polymers and by little amounts of ions inc luded in them. The formation of an aluminium hydroxide layer, electronic in sulator but ion conductor, at the Al/polymer interface was hypothesised to justify that both a battery in the dark and a photoelectrochemical cell can be established. (C) 1998 Elsevier Science S.A. All rights reserved.