Improving Carrier Mobility of Near-Amorphous Donor-Acceptor Conjugated Polymer Thin Films via Promoting Intensive and Continuous Polymer Aggregations

For near-amorphous donor-acceptor (D-A) polymers, local aggregates can serve as charge transport contacts between conjugated backbones, which are important for achieving high carrier mobility of polymer films as optoelectronic materials. However, regulating the aggregation density and continuity of near-amorphous conjugated polymers remains significantly challenging because of complex interactions between polymers and processing solvents. To address this issue, we propose a strategy to effectively promote the continuous aggregations of poly(indacenodithiophene-co-benzothiadiazole) (IDTBT) by providing more space for polymer chain movement. Specifically, an optimized amount of chlorohexadecane was added into an IDTBT chlorobenzene (CB) solution, and the subsequent spin-coated polymer film was further annealed at 150 °C for 30 min. Chlorohexadecane can act as a spacer molecule that significantly increases the distance between IDTBT chains due to its strong interaction with both the polymer backbone and side chain. During annealing, the chlorohexadecane additive volatilizes and leaves large space, which further promotes the self-assembly of IDTBT polymer chains into a coarse fiber-like network through effective π-π interactions. The IDTBT films obtained using this strategy show much more apparent backbone aggregates in both size and continuity than those in both pristine (without additives) and nonannealed (with additives) films. Furthermore, physicochemical features in these films were verified by the characterization of ultraviolet-visible (UV-vis) spectra, grazing-incidence wide-angle X-ray scattering (GIWAXS), atomic force microscopy (AFM), and molecular dynamics simulations. The average carrier mobility (μ_ave) of 1% chlorohexadecane-treated IDTBT films after annealing reaches 3.61 ± 0.09 cm² V^-1 s^-1, 2-fold higher than that of annealed CB films.