Short-range aggregation regulation of conjugated polymers: high mobility and cyclic tensile stability driven by chemical crosslinking†

Abstract

Conjugated polymer films show great potential in wearable electronics. However, it is challenging to maintain the initial electrical performance of conjugated polymer films during cyclic stretching. Herein, we modulate the electrical and mechanical properties of a conjugated polymer poly(indenothiophene-co-benzothiadiazole) (IDTBT) by chemical crosslinking with a small molecule (((oxybis(ethane-2,1-diyl))bis(oxy))bis(4,1-phenylene))bis(phenylmethanone) (BP), aiming to improve the electrical stability during cyclic stretching. Under ultraviolet illumination, BP with two benzophenone end groups can form high-activity biradicals to abstract the aliphatic hydrogens on the alkyl sidechains of IDTBT, producing a crosslinked film. Compared to the pristine film, the crosslinked film shows decreased long-range ordering but tightly packed π–π stacks with more co-planar backbones. During stretching, the flexible oligomeric (ethylene glycol) linkers enhance the conformational freedom of polymer chains and the chemical crosslinking prevents irreversible chain slippage, significantly enhancing cyclic stretchability. Meanwhile, the physical crosslinked short-range ordered aggregates provide efficient charge transport channels. Consequently, the crosslinked film shows the charge carrier mobility of 0.92 ± 0.03 cm² V⁻¹ s⁻¹ at 100% strain and the nearly constant mobility of 0.86 ± 0.04 cm² V⁻¹ s⁻¹ after cyclic stretching-releasing at 30% strain for 1000 times.