Quantification of tie-chain content in semicrystalline conjugated polymers and its impact on charge transport

Polymer tie-chains connect adjacent crystalline domains and strongly impact charge transport in semicrystalline conjugated polymers. To assess their role in charge transport, we blended 100% regioregular narrowly-dispersed poly(3-hexylthiophene), or P3HT, having an M_n of 5 kg/mol with a high-MW counterpart having an M_n of 40 kg/mol. Varying the high-MW fraction in the homopolymer blends allows tuning of the tie-chain content, which we quantified with the Primary Structure Parameter (PSP) model, originally developed to correlate crack resistance of polyethylene resins with their microstructure. The charge-carrier mobility of transistors comprising P3HT blends increases with increasing loadings of the high-MW P3HT. We attribute this observation to enhanced interdomain connectivity indicated by higher PSP. Beyond the percolation threshold for macroscopic charge transport, the mobility plateaus because charge transport beyond this point is limited by local structural disorder within P3HT crystalline domains, as evidenced by X-ray paracrystallinity analysis. Our results quantify the role of interdomain connectivity and demonstrate its interplay with local structural disorder in determining charge-transport characteristics in semicrystalline conjugated polymers.