Inter-chain Coupling On The Kinetic Processes Of Photoexcitation In The Polymer

Within an extended Su-Schrieffer-Heeger model including interchain interactions, the dynamics of photoexcitations in two coupled conjugated polymer chains is investigated by using a nonadiabatic evolution method. For intrachain photoexcitation, the dynamical evolution of lattice on the chain of photoexcitation is similar to the case of a single chain with weaker interchain coupling, the output is a mixed state including both intrachain polaron-exciton and intrachain oppositely charged polaron pairs. With the increasing of interchain interactions ( t_⊥), the amplitude of the distortions on the photoexcited chain decreases, at the same time, which on the other chain increases gradually. Until strong interchain coupling ( t_⊥>0.25eV), the deformations on the two chains have almost the same amplitude. Except the two kinds of stable states on each chain, i.e., the intrachain exciton and the interchain charged polaron pairs, the interchain polaron-exciton and the interchain separated charged polaron pairs are obtained. The maximum yield of charged polarons and interchain polaron-exciton is about 25% and 37.5% respectively. Additionally, the conjugation length of polymers plays an important role in understanding the photogeneration of charge carriers. The dynamics of interchain photoexcitation, where an electron is excited from one chain to the other chain, is also investigated. It is interesting that the centers of two polarons do not concide and be separated. So this photoexcitation is propitious to the photogeneration of charge carriers (charged polarons). The dynamics of the intrachain and interchain polaron-exciton dissociation induced by an external electric field is also investigated. Our simulational results show that: With strong fields 10 mV/(A|°), the intrachain polaron-exciton will be dissociated to an oppositly charged polaron pairs. With critical electric field, the interchain polaron-exciton will be dissociated to one positively and one negatively charged polarons, which finally locate at opposite chains ends respectively. The calculated result indicate the process that interchain polaron-exciton is dissociated by electronic field is easier than that of intrachain polaron-exciton. So the charged carriers are generated easily.