Kinetically Controlled Phase Separation Governing Hole Transport in Conjugated Polymer/Insulating Polymer Blend Films

ABSTRACT Blending insulating polymers with conjugated polymers has been reported to significantly improve charge transport in thin films by modifying molecular aggregation and film morphology. However, the underlying mechanism for this improvement is still not fully understood. Herein, we investigate the charge transport properties of a thiophene‐based conjugated polymer (J61) blended with two insulating polymers, polystyrene (PS) and cyclic olefin copolymer (ZEONEX), which possess distinct solubility parameters. Particular attention is paid to film‐formation kinetics and the resulting phase‐separated structures. We find that blending J61 with PS significantly shortens the solidification time of J61 domains and more effectively suppresses the formation of H‐aggregates compared to blending with ZEONEX. This rapid solidification kinetically preserves the solution‐state planar backbone conformation of J61, resulting in superior hole mobility relative to both the J61 neat film and J61/ZEONEX blend film. These findings provide mechanistic insights into how insulating polymers regulate film‐formation kinetics and molecular aggregation, offering a rational strategy for enhancing charge transport in conjugated polymers through controlled phase separation.