Intra-Island Coulomb Correlations in PEDOT:PSS Thin Films; Saturation of Spin Polarization Magnetoresistance

Magnetic field and temperature dependence of the magneto-conductance (MC) of thin films made of self-p-doped poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) having room temperature conductivity of ≈200 S cm⁻¹ in the range of fields B = 0–14 T and temperatures T = 1.8–300 K are reported. At B = 0 and for current parallel to the film surface, the conductance follows a variable range hopping mechanism in two dimensions. It is shown that the finite Coulomb correlations, U, within the nano-crystalline PEDOT islands dominates MC at low temperatures and high fields. At T = 1.8 K, the intra-island Coulomb correlation spin polarization mechanism is already saturated for B > 10 T establishing a finite minimum of ≈2 meV for U. This small value of U is in line with the delocalized nature of the holes within the PEDOT islands and the relatively high conductivity that makes it essential in organic opto-electronics.