Intrachain Aggregation of Charge-Transfer Complexes in Conjugated Polymer:Acceptor Blends from Photoluminescence Quenching

Recent studies of conjugated polymer donor–acceptor blends show that the donor and acceptor can form a weak charge-transfer complex (CTC) in the electronic ground state, and these CTCs can significantly change the photophysics in the blend. In this work, we study photoluminescence quenching in model polymer acceptor blends of poly(methoxy,5-(2′-ethyl-hexyloxy-1,4-phenylene-vinylene)) (MEH-PPV) with TNF (2,4,7-trinitrofluorenone) in solution. Our experimental data show that the observed strong increase in the CTC concentration with acceptor content results only in a moderate quenching enhancement. We propose an extended Stern–Volmer relation to model photoluminescence quenching in conjugated polymers with statistically homogeneous distribution of CTCs over polymer chains. We compare the experimental data with the model and conclude that the CTCs are not randomly distributed within a chain but form intrachain CTC clusters. These findings imply that the CTCs can influence the morphology of donor–acceptor blends, which is of paramount importance for the performance of organic solar cells.