The influence of polymer nanomorphology on exciton dynamics: a computational study

Abstract

One of the great advantages in using semiconducting polymers as part of the active component in organic solar cells is the fact that they can be processed in solution. However, due to its nature, the long polymer chains present in the active layer tend to bend/twist in order to achieve a more favourable energetic configuration (Sumpter, et al. 2005). In this way, the polymer film can be seen as an ensemble of straight conjugated segments with different lengths connected by structural defects or by weak Van der Waals bonds, with each segment behaving like a chromophore. In the last years it turns out clear that the arrangement of the conjugated segments in the bulk (i.e. the polymer morphology at nanoscale) is one the main factors that influence the physical processes that are behind the functioning of polymer-based optoelectronic devices (Moliton, et al. 2006), namely exciton dynamics. After photon absorption by a conjugated segment, a quasi-particle, known as intramolecular singlet exciton, is formed, which presents a high binding energy, a long life-time and with the ability to diffuse in these 3D polymer networks. In order to improve polymer-based solar cells efficiency, is important to understand how polymer nanomorphology influences the exciton diffusion process.