Abstract
AbstractThe electrochemical dedoping and redoping processes of a thin poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film immersed in an electrolyte are studied at different temperatures with time‐resolved spectroelectrochemistry in the visible and near‐infrared range. The spectral signatures of neutral, polaronic, and bipolaronic states of PEDOT are resolved using multivariate curve resolution analysis. Kinetic modeling of their dynamics reveals that both the dedoping and redoping are sequential processes and occur within a few hundred milliseconds in the system. Evaluation of the temperature‐dependence with the Van't Hoff, Arrhenius, and Eyring formalisms highlights the role of entropy in both the establishment of the redox equilibrium at a given voltage bias and the reaction rates. This study provides a significant understanding of the fundamental mechanisms determining the level and rate of the electrochemical processes in PEDOT:PSS and will help tailor the design of faster and more efficient bioelectronic devices based on mixed ionic–electronic conductors.
Highlights
Organic mixed ionic–electronic conductors (OMIECs) are materials with the ability to conduct both electronic and ionic is applied (Vbias > 0), redoping of the film occurs as positively charged ions are expulsed from the film and the PSS− matrix is decompensated by oxidization of PEDOT0 and PEDOT+ to respectively PEDOT+ and PEDOT2+.[8,9,10,14]
The dedoping is driven by enthalpy, while the redoping is driven by entropy
One hypothesis that we propose here is that a certain concentration of polarons (reached at t(′)onset) is necessary to induce large-range structural changes in the packing of the PEDOT chains, such as have been observed during the B → P conversion by time-resolved Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS) measurements,[10] and that those morphological changes are needed before the redox step can proceed toward the final equilibrium
Summary
Organic mixed ionic–electronic conductors (OMIECs) are materials with the ability to conduct both electronic and ionic is applied (Vbias > 0), redoping of the film occurs as positively charged ions are expulsed from the film and the PSS− matrix is decompensated by oxidization of PEDOT0 and PEDOT+ to respectively PEDOT+ and PEDOT2+.[8,9,10,14] We note a debate charges within their bulk.[1,2] Among these materials, poly(3,4- about the nature of PEDOT2+, which is sometimes defined as ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) a bipolaron and sometimes as a polaron pair.[14] Resolving this is the most investigated It is transparent, flexible, very conduc- controversy is beyond the scope of our work and the term bipotive, and benefits from a high biocompatibility and commercial laron will be used as it is more prominent in the literature.
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