Systematic Investigation of Side-Chain Branching Position Effect on Electron Carrier Mobility in Conjugated Polymers

Recently, polymer field-effect transistors have gone through rapid development. Nevertheless, charge transport mechanism and structure-property relationship are less understood. Here we use strong electron-deficient benzodifurandione-based poly(p-phenylene vinylene) (BDPPV) as polymer backbone and develop six BDPPV-based polymers (BDPPV-C1 to C6) with various side-chain branching positions to systematically study the side-chain effect on device performance. All the polymers exhibited ambient-stable n-type transporting behaviors with the highest electron mobility of up to 1.40 cm 2 V-1 s(-1). The film morphologies and microstructures of all the six polymers were systematically investigated. Our results demonstrate that the interchain pi-pi stacking distance decreases as moving the branching position away from polymer backbones, and an unprecedentedly close pi-pi stacking distance down to 3.38 angstrom is obtained for BDPPV-C4 to C6. Nonetheless, closer pi-pi stacking distance does not always correlate with higher electron mobility. Polymer crystallinity, thin film disorder, and polymer packing conformation, which all influenced by side-chain branching position, are proved to show significant influence on device performance. Our study not only reveals that pi-pi stacking distance is not the decisive factor on carrier mobility in conjugated polymers but also demonstrates that side-chain branching position engineering is a powerful strategy to modulate and balance these factors in conjugated polymers.