Interplay Between Microscopic Structure and Intermolecular Charge-Transfer Processes in Polymer-Fullerene Bulk Heterojunctions

We provide an overview of the development and application of nonconventional techniques that allowed us to probe the molecular excited states in conjugated polymers with respect to their molecular orientation and the nanomechanical properties of the topmost surface layer. To probe triplet and charge-transfer excited states and their fate, we applied the optically detected magnetic resonance technique extended for angular resolution. The surface morphology and three-dimensional depth profiles of the topmost surface layer were obtained with multi-set point intermittent contact mode atomic force microscopy. These studies were performed on model systems such as poly(3-hexylthiophene) as well as on the novel, low-bandgap copolymer poly [(4, 8-bis-(2-ethylhexyloxy)-benzo(1,2-b: 4,5-b9) dithiophene)-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[ 3,4-b] thiophene-)-2-carboxylate-2-6-diyl)].