Electronic properties of junctions between aluminum and neutral or doped poly[3-(4-octylphenyl)-2,2'-bithiophene]

A Schottky contact is made from the polymer poly[3-(4-octylphenyl)-2,2'-bithiophene] PTOPT, in its neutral state and doped with PF6- and a low work function metal (Al). The electrical properties have been investigated by means of current-voltage (I-V) and capacitance-voltage (C-V) measurements. In the sandwich structure of ITO/PTOPT/Al, the neutral polymer rectifies by five orders of magnitude, while the doped diodes yield three orders of magnitude. Doping of the polymer is verified using optical spectroscopy. I-V, C-V and complex impedance techniques are used to analyze the Schottky barrier characteristics. The diode quality factor n is 1.2 for the neutral and 4.2 for the doped samples. The dopant concentrations of doped and undoped diodes differ by about a factor of two, which is probably due to dedoping of the polymer close to the interface upon Al deposition.