Semiconducting polymers have the potential to be used in an exciting array of devices, but their intrinsic conductivity is low due to their large band gaps. Chemically doping conjugated polymers is an effective way to increase conductivity and involves treating the polymer with a strong electron acceptor or donor that can undergo charge transfer (i.e., redox) with the polymer. The charge transfer reaction creates delocalized electrical carriers on the polymer chain (usually positive polarons, a.k.a. holes) while the dopant molecules remain in the film and serve as counterions. Unfortunately, the strong electrostatic attraction between polarons and most dopant counterions will localize the polarons and reduce their mobility. Here, we first explore how polymer and dopant structure can be used to mitigate that electrostatic attraction.  One example is the use of dopants based on substituted icosahedral dodecaborane (DDB) clusters that provide a unique combination of high oxidizing potential and large size.  By tuning the cluster redox potential, we can understand the role of energetics in polymer conductivity, and the large size helps to reduce electrostatic interactions, resulting in polymer films with highly delocalized polarons and thus high conductivity.  Polymer crystallinity and crystal structure provides another key way to tune dopant-counterion interactions.  A combination of molecular substituent tuning, electronic spectroscopy, and X-ray scattering are combined with both chemical and electrochemical doping to understand chemical-structure-function relationships.  We next consider applications for electrochemically-doped conjugated polymers as binders in lithium ion batteries.  Battery binders are usually chosen only for chemical inertness, but the use of conjugated polymer binders can increase overall conductivity and thus rate capabilities.  By tuning the polymer redox to match the electrode material, highly conductive doped binders can be produced, and by tuning the side chains, ionic conductivity can be mixed with electronic conductivity, both of which are needed for fast battery operation.

Understanding and exploiting redox in conjugated polymers: From improved polymer conductivity to next-generation polymer binders for lithium ion batteries

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