Influence of the doping of the polymer on the dark and photoelectrical properties in the junction ITO/poly(4,4′-dipentoxy-2,2′-bithiophene)/aluminium

The transport properties of the system, ITO/poly(4,4′-dipentoxy-2,2′-bithiophene)/aluminium, were investigated both in the dark and under white light illumination for three different oxidation states of the polymer. A deterioration of both the rectification properties in the dark and the photovoltaic performances was observed by increasing the doping level. The less-doped junction was tested in photoconductive mode and an exponential relationship was found between the photosensitivity and the reverse voltage applied to the junction. A photosensitivity of the order of 10−3 A W−1 was achieved for an applied voltage as low as 2 V over the full range of the incident power intensity (0.4–33 mW cm−2).