Benzothiadiazole bridged EDOT based donor–acceptor polymers with tunable optical, electrochemical, morphological and electrochromic performance: effects of solvents and electrolytes

Abstract

Donor–acceptor (D–A) polymers have been widely studied for their tunable electronic properties, however, it is surprising that systematic studies on the effect of different solvents and electrolytes on their opto-electrochemical, morphological and electrochromic performance have drawn only little attention. In the presented work, nine different D–A polymer films, poly(4,7-di(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)benzo[1,2,5]thiadiazole) (a-i-P1), were electrosynthesised using different polar solvents (PC, MeCN and DCM) and supporting electrolytes (TBAPF₆, TBAClO₄ and TBABF₄). A thorough study of these D–A polymer films using cyclic voltammetry, UV-Vis-NIR spectroscopy, FE-SEM, spectroelectrochemistry and electrochromic techniques has been performed. We found a significant effect of both the supporting electrolytes and solvents on the morphology of polymer films which correlates well with their opto-electronic properties. Films prepared using the TBAClO₄/PC system show a smooth morphology with a significantly high coloration efficiency of 264 cm² C⁻¹ and an optical contrast of 65.3%. Such differences in the optical and electrochemical properties of polymer films were explained by the ion pair formation during polymerisation.