Backbone Engineering of Diketopyrrolopyrrole-Based Conjugated Polymers through Random Terpolymerization for Improved Mobility–Stretchability Property

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Abstract

Conjugated polymers synthesized through random terpolymerization have recently attracted great research interest due to the synergetic effect on the polymer's crystallinity and semiconducting properties. Several studies have demonstrated the efficacy of random terpolymerization in fine-tuning the aggregation behavior and optoelectronic property of conjugated polymers to yield enhanced device performance. However, as an influential approach of backbone engineering, its efficacy in modulating the mobility-stretchability property of high-performance conjugated polymers has not been fuller explored to date. Herein, a series of random terpolymers based on the diketopyrrolopyrrole-bithiophene (DPP-2T) backbone incorporating different amounts of isoindigo (IID) unit are synthesized, and their structure-mobility-stretchability correlation is thoroughly investigated. Our results reveal that random terpolymers containing a low IID content (DPP95 and DPP90) show enhanced interchain packing and solid-state aggregation to result in improved charge-transporting performance (can reach 4 order higher) compared to the parent polymer DPP100. In addition, owing to the enriched amorphous feature, DPP95 and DPP90 deliver an improved orthogonal mobility (μ_h) of >0.01 cm2 V-1 s-1 under a 100% strain, higher than the value (∼0.002 cm2 V-1 s-1) of DPP100. Moreover, DPP95 even yields 20% enhanced orthogonal μ_h retention after 800 stretching-releasing cycles with 60% strain. As concluded from a series of analyses, the improved mobility-stretchability property exerted by random terpolymerization arises from the enriched amorphous feature and enhanced aggregation behavior imposed by the geometry mismatch between different acceptors (DPP and IID). This study demonstrates that backbone engineering through rational random terpolymerization not only enhances the mobility-stretchability of a conjugated polymer but also realizes a better mechanical endurance, providing a new perspective for the design of high-performance stretchable conjugated polymers.

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