(630b) Toward Physical Models of Thermoelectric Transport Rules At the Organic-Inorganic Interface

The thermoelectric properties of solution-processed conducting polymer/nanoparticle composite films have been a focus of interest for many groups due to their unique transport mechanisms, enabling new modalities of transport which can surpass common optimization dilemmas in inorganic thermoelectrics.  However, many interesting reports have lacked a theoretical framework to guide materials design.  Here, I present a few organic/inorganic thermoelectric model systems studied as a function of nanoparticle loading and chemical doping.  We use these to develop phenomenological frameworks to guide engineering of this novel material class. 

Here I will discuss two different hybrid systems, and the tunability and optimization of their thermoelectric performance:  1.) Poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and Tellurium nanowire devices, and  Polyaniline and nanoparticle-Titania devices.  For each of these systems, interesting non-monotonic electrical conductivity is observed at intermediate loadings, suggesting non-effective medium behavior, in contrast to the values of the Seebeck coefficient increase linearly with mass fraction of inorganic.  These trends in Seebeck coefficient and electrical conductivity lead to an optimized power factor in the composites that exceed that of the individual components. The surprising electrical conductivity behavior can be explained with a mixing model where carrier transport is primarily through a highly conductive volume of polymer that exists at the nanoparticle-polymer interface.  We have developed a general phenomenological model for these systems suggesting that this increase in conductivity results from a structural modification of the polymer, and elucidates a novel route for optimizing transport in nanoscale organic/inorganic composites.