Charge transport and energetic disorder in polymer: fullerene blends

Mobility versus temperature measurements on two different polymer: fullerene blends intended for solar cell applications have been evaluated in terms of the energetic disorder and how this varies with stoichiometry. The charge transport is shown to be confined to the intended phases in both cases, but with fundamentally different interaction properties. In one case the energetic disorder is a function of stoichiometry for the hole transport, while it is constant and equal to that of the pure fullerene for electrons, and in the other case it is the hole transport that has a stoichiometry independent energetic disorder. Transport site dilution is argued to be present in the fixed energetic disorder system and this is offered as a partial explanation to molecular weight dependent currents in solar cells. Determination of the glass transition temperature through the use of field effect transistors is also demonstrated. (C) 2010 Elsevier B.V. All rights reserved.