Solvent-Tuned Aggregation and Its Limited Functional Impact in a Rigid-Rod Indacenodithiophene-Benzothiadiazole Copolymer.

Abstract

We investigate the influence of solvent quality on solution-state aggregation and solid-state morphology in a rigid indacenodithiophene-based donor-acceptor copolymer, PIDTC16-BT. Using UV-vis spectroscopy and temperature-dependent small-angle X-ray scattering (SAXS), we characterize aggregation behavior across three solvents of varying segmental compatibility. Anisole promotes rapid, cooperative aggregation with lamellar ordering, while toluene and tetrahydrofuran (THF) support more gradual or dispersed clustering. Grazing-incidence small-angle X-ray scattering (GISAXS) reveals that these solution-state differences partially translate into solid-state packing, with anisole-cast films exhibiting enhanced lamellar coherence and backbone alignment. Despite these structural variations, organic field-effect transistor (OFET) measurements show comparable hole mobilities across all solvents. These results suggest that backbone rigidity and kinetic trapping during casting suppress the functional impact of solvent-driven aggregation. Segment-specific solubility analysis using Hansen parameters provides a framework for understanding aggregation pathways in rigid D-A systems. Our findings highlight the morphological robustness of PIDTC16-BT and underscore the need for multiscale characterization when linking processing to performance in conjugated polymer devices.