Influence of Energy Landscapes, Charge-Carrier Mobilities, and Morphology on the Thermoelectric Properties of Pi-Conjugated Polymer Blends

Conjugated polymers are emerging as attractive low-cost thermoelectric materials with flexible form factors, and further performance improvements will make them appealing for applications such as recovering low-grade waste heat, powering wearable electronics based on body heat, or enabling low-cost refrigeration. Significant thermoelectric performance improvements for ?-conjugated polymers are likely to arise from increases in electrical conductivity and the Seebeck coefficient. We hypothesize that the Seebeck coefficient can be significantly increased with minimal decreases in electrical conductivity by blending high and low mobility polymers together and introducing an energy offset between the transport states of the different polymers. This strategy is expected to enhance the contribution of higher energy charge-carriers to the electrical conductivity, thereby increasing the Seebeck coefficient. Combined with appropriate film morphologies, we expect that the thermoelectric performance of these blends will exceed both of the pure polymers. In the proposed research we will experimentally investigate the Seebeck coefficient and electrical conductivity in polymer blends, whereby the polymers possess widely differing charge-carrier mobilities and transport energy levels. We will experimentally measure the charge-carrier mobilities using field-effect transistors, the energy offsets between polymers using a custom ultraviolet photoemission spectroscopy system, and film morphologies with transmission electron microscopy to determine how these variables contribute to the experimentally measured Seebeck coefficients. We expect that the increased fundamental understanding gained through this work will enable the more rapid development of organic thermoelectrics using this polymer blend approach.