The isokinetic temperature in disordered organic semiconductors

We have investigated the field dependence of the in-plane conductivity in p oly(2,5-thienylene vinylene) thin films. The conductivity is found to have a square root dependence on the lateral electric field with values of the a ctivation energy, Delta =0.46 eV, B=2.3 . 10(-5) eV(m/V)(1/2) and the chara cteristic temperature T-0=5.2 . 10(2) K. A similar value (T-0=4.9 . 10(2) K ) is found for the isokinetic temperature in Meyer-Neldel experiments on po ly(2,5-thienylene vinylene) field-effect transistors. Based on these result s, we argue that entropy changes due to hopping of charge carriers should b e incorporated in theoretical descriptions of the field dependent mobility in disordered organic semiconductors.