Influence of the bridging atom on the electrochromic performance of a cyclopentadithiophene polymer

In this article, carbon- (PCPDTTBT) and silicon-bridged (PSiPDTTBT) cyclopentadithiophene (CPDT)-based polymers have been synthesized. We have systematically studied the effect of replacing a carbon atom with a silicon atom on the main chain of the conjugated polymer and the optoelectronic properties. With the simple substitution, the results indicate that the PSiPDTTBT reveals a higher crystallinity, improved thermal stability, charge transport properties, and lower resistance at the polymer-electrolyte interface. As a result, the PSiPDTTBT exhibits better electrochromic properties including higher contrast and coloration efficiency (CE) with respect to its carbon analogs. We attribute this better electrochromic performance to the presence of strong π-π stacking in the silicon-bridged CPDT-based polymer. The PSiPDTTBT shows a transmittance window of 55.5% at 560 nm and CE of 434 mC/cm².