Exciton Structure and Dynamics in Solution Aggregates of a Low-Bandgap Copolymer

In this work, we elucidate exciton structure, dynamics, and charge generation in the solution phase aggregates of a low-bandgap donor-acceptor polymer, poly(4,8-bis-alkyloxybenzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-(alkylthieno[3,4-b]thiophene-2carboxylate)-2,6-diyl (PBDTTT). The polymer aggregates in the solution phase serve as precursors for thin film morphologies. We have identified intrachain and interchain exciton transitions and resolved their relaxation pathways by comparing excitons in solution aggregates to those in isolated polymer chains. Hot intrachain excitons have led to the generation of stabilized interchain charge-separated states in solution aggregates, which could serve as the intermediate state to the hot exciton charge separation in bulk heterojunctions (BHJs). These results have important implications for controlling morphology dependent exciton dynamics in solution processed BHJs.