In π-conjugated polymers for photovoltaic applications, intrinsic conjugation defects are known to play crucial roles in impacting exciton transport after photoexcitation. However, the understanding of the associated microscopic processes still remains limited. Here, we present a theoretical investigation of the effects of different conjugation defects on the dynamics of exciton transport in two linearly coupled poly(p-phenylene vinylene) (PPV) molecules. The model system is constructed by employing an extended version of the Su-Schrieffer-Heeger model and the exciton behaviors are simulated by means of a quantum nonadiabatic dynamics. We identify two types of conjugation defects, i.e., weakening conjugation and strengthening conjugation, which are demonstrated to play different roles in impacting the dynamics of exciton transport in the system. The weakening conjugation acts as an energy well inclined to trap a moving exciton, while the strengthening conjugation acts as an energy barrier inclined to block the exciton. We also systematically simulate both intrachain and interchain dynamics of exciton transport, and find that an exciton could experience a "short-time delaying", "trapping", "blocking", or "hopping" process, which is determined by the defect type, strength, and position. These findings provide a microscopic understanding of how the exciton transport dynamics can be impacted by conjugation defects in an actual polymer system.

Experimental verification for ultrafast charge generations is a significant advancement in recent studies of polymer solar cells, but its underlying mechanism still remains unclear. In this paper, a new mechanism of ultrafast charge generation is proposed, where a local nonuniform electric field plays a vital role. We systematically simulate the exciton dissociation dynamics along a polymer chain with electric field linearly distributed. The polymer chain can be divided into two regions according to the exciton dissociation degree, i.e., complete dissociation region and partial dissociation region. In the former, a photogenerated exciton can dissociate directly and completely into free charges. In the latter, however, a photogenerated exciton first experiences an ultrafast migration process toward the complete dissociation region and then partially dissociates with fractional free charge generation. In most of our simulations, the exciton dissociation can take place within a time scale of 1 ps, contributing to the ultrafast charge generation.

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We theoretically study the geometric effect of quantum dynamical evolution in the presence of a nonequilibrium noisy environment. We derive the expression of the time dependent geometric phase in terms of the dynamical evolution and the overlap between the time evolved state and initial state. It is shown that the frequency shift induced by the environmental nonequilibrium feature plays a crucial role in the geometric phase and evolution path of the quantum dynamics. The nonequilibrium feature of the environment makes the length of evolution path becomes longer and reduces the dynamical decoherence and non-Markovian behavior in the quantum dynamics.

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