Determination of the mechanism behind the organic magnetoresistance (OMAR) effect by using impedance spectroscopy

We investigated the organic magnetoresistance (OMAR) mechanism in poly(3–hexylthiophene–2,5–diyl) (P3HT)–based diodes, by using impedance spectroscopy. We have prepared layered structures consisting of indium tin oxide, poly(3,4–ethylenedioxythiophene):poly(styrenesulphonate) (PEDOT:PSS), P3HT and aluminium and measured the bias voltage dependence of the OMAR and of the impedance spectra. The capacitance deduced from the impedance data indicated that the OMAR was explained by the single–carrier (bipolaron) model at lower bias voltages as well as double–carrier models at higher bias voltages. The impedance response also suggested that the OMAR from the single–carrier model was governed by the PEDOT:PSS/P3HT interface whereas the double–carrier OMAR was mainly related to the P3HT layer.