Controlling the Mode of Operation in Polymeric Thermoelectrics Through Polymeric Ionic Liquid-gated Transistors

Studying the thermoelectric properties of organic semiconductors is an emerging way to understand interplay between ions and electrons, as it provides an independent measurement technique to ascertain transport properties. Conventional vapor- and solution-phase doping increase electrical conductivity (σ) by increasing carrier concentration (n), but morphological changes created by dopant infiltration complicates the interpretation of results. We have utilized a field-effect transistor geometry to control ion infiltration in a p-type semiconducting polymer via gating. Polymeric Ionic Liquids (PILs) are high-capacitance polymers containing tethered ionic liquid-like moieties. To study the effect of dopant infiltration on charge transport in the high carrier concentration regime, we employed a PIL as the gate dielectric, where the degree of infiltration is tuned by tethering either the anion or cation in the PIL. The transistor geometry allows for n, thermopower (S), and σ to be determined experimentally, offering a straightforward method to explore thermoelectric transport. Our studies demonstrate that gating with PILs offers a novel strategy to deconvolute charge transport and microstructure and guide development in these systems.