Influence of Donor–Acceptor Arrangement on Charge Transport in Conjugated Copolymers

The intramolecular arrangement of the donor (D) and acceptor (A) moieties can greatly influence the electronic properties of D–A conjugated copolymers. Here, we report a comparative study on a class of copolymers with either alternatively or randomly arranged D and A moieties. Through combination of the grazing incidence X-ray scattering, charge modulation spectroscopy and temperature-dependent field-effect mobility measurement, we provide direct evidence that the alternating D–A arrangement generates a relatively high degree of crystallinity, resulting in predominant two-dimensional delocalization of polaronic charge carriers, low energetic disorder, and thus good charge-transport property. On the other hand, the randomly arranged D–A structure, although providing broad-band absorption, gives rise to short-range ordered aggregates surrounded by amorphous region. Accordingly, a transition from a delocalized to a localized polaronic regime is observed as the charge carrier concentration increases, and disorder broadening of density of states is also revealed.