Estimation of hole injection barrier at the poly-3(hexylthiophene)/metal interface using accumulated charge measurement

Abstract

Abstract Hole injection barriers at the regioregular-poly-3(hexylthiophene) (RR-P3HT)/metal (Cu or Ag) interface were investigated using the accumulated charge measurement (ACM). Thermal annealing of RR-P3HT at 55 °C decreased the injection barrier. RR-P3HT thermally annealed in N2 forms an ohmic contact with Ag and a Schottky contact with Cu. The obtained values of the injection barriers, ϕB were well expressed by the Mott-Schottky rule, i.e., ϕB = IE - Wm′, where IE is the ionization energy of RR-P3HT and Wm′ is the work function of the metal electrode in air. The effect of the large vacuum level shift, reported in UPS studies conducted under ultrahigh vacuum, was not observed.