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

• The cyclopentadithiophene based polymer has been synthesized.
• The effect of bridging atom has been investigated.
• We compared the silicon and carbon-bridged polymer.
• The silicon-bridged polymer reveals better electrochromic property.

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.