The influence of charge trapping on the electrochromic performance of poly(3,4-alkylenedioxythiophene) derivatives

This paper describes the electrochromic properties of a series of poly(3,4-alkylenedioxythiophene) (PXDOT) derivatives featuring various ring sizes and substitutions. The presence of a bulky group on the monomer resulted in a polymer possessing a more-open morphology, which promoted reversible ionic transfer. We used an electrochemical quartz crystal microbalance and cyclic voltammetry to investigate the properties of these polymers. We found that both cations and anions were involved in the charge compensation process. Furthermore, PXDOT derivatives possessing larger ring sizes and/or longer alkyl substituents exhibited less trapping of ions within the polymer during the redox process. The long-term electrochromic stability of these PXDOTs depended strongly on the number of trapped ions. Although the transmittance attenuation of poly(3,4-ethylenedioxythiophene) (PEDOT) decreased from 53 to 42%, we observed no significant decay for poly(diethyl-3,4-dihydro-2H-thieno[3,4-b]-[1,4]dioxepine) (PProDOT-Et(2)) after 400 cycles.