Synergistic Effects of Insulating Polystyrene on Hole Transport in Crystalline Conjugated Polymers

The morphology of conjugated polymers plays a significant role in determining their charge transport characteristics. In this study, we investigate the hole transport properties of a crystalline conjugated polymer (PBDB-T) blended with an insulating polystyrene (PS) with different molecular weights and weight fractions. Surprisingly, PBDB-T/PS blend films exhibit enhanced hole mobility compared to the PBDB-T neat films. This enhancement is strongly correlated with morphological changes in PBDB-T, which are dependent upon the molecular weight of the PS matrix. Specifically, blending with low molecular weight PS promotes homogeneous mixing and increased crystallinity, leading to a moderate improvement in the charge transport. In contrast, blending with high molecular weight PS induces phase separation, resulting in the formation of PBDB-T rich domains. These domains enable efficient charge percolation through localized aggregation and by reducing trap densities. These findings underscore the dual role of insulating polymers in modulating phase-separated structures and charge transport pathways in conjugated polymer systems. The results demonstrate that morphology engineering via polymer blending offers a simple yet powerful strategy for optimizing charge transport, which in turn offers promising avenues for the advancement in flexible optoelectronic devices.