Carrier-carrier Coulomb interactions reduce power factor in organic thermoelectrics

Abstract

Organic semiconductors are excellent candidates for low temperature thermoelectric generators. However, such thermoelectric applications require materials be doped and highly conductive. Here, we show how doping affects the Seebeck coefficient in organic semiconductors using kinetic Monte Carlo simulations. Employing a hopping transport approach, we demonstrate that at high dopant loading, carrier-carrier interactions can reduce the Seebeck coefficient. This results in systems with intrinsic disorder, still following Heike's formula for thermopower at high dopant density. Reducing these carrier-carrier interactions results in an increased Seebeck coefficient and power factor. Specifically, a realistic reduction in carrier-carrier interactions can increase the power factor by more than a factor 15, increasing ZT above 1 for organic thermoelectrics.