Altering the Microstructure of Conjugated Polymers in Solution via Microwave Irradiation

Solution-processed conjugated polymers can exhibit high charge carrier mobilities depending on the microstructure of the resultant films. Controlling the solution-state aggregation, however, remains challenging for mass production. Through the application of microwave (MW) heating, we demonstrate that poly-[N,N'-bis-(2-octyldodecyl)-naphthalene-1,4,5,8-bis-(dicarboximide)-2,6-diyl]-alt-5,5'(2,2'bithiophene) P(NDI2OD-T2) solution in chlorobenzene can impart a dramatic improvement in the microstructure of the thin film, rendering transistor devices with highest saturation field-effect mobility values of 0.45 cm² V^-1 s^-1. Here, by employing in situ optical spectroscopies and small-angle X-ray scattering (SAXS) techniques, we elaborate the controllable swelling-collapsing dynamics of a polymer solution into ordered aggregates under MW heating. The in situ optical measurements, including absorption and photoluminescence (PL), reveal distinguished features of the intra/intermolecular ordering of polymer chains, while the in situ SAXS unveils the effectiveness of MW heating in reordering the swollen coils. As a result, MW heating offers rapid operation, high-energy efficiency, and scalable fabrication, and it is a versatile technique enhancing charge transport of the final thin films, regardless of their casting processes and conjugated polymer structures. This finding may shed insight into the mechanism of reordering aggregation on conjugated polymer solutions under MW irradiation for further research and development in related fields.