Thermoelectric Properties of Doped Organic Semiconductors

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NON-TECHNICAL SUMMARYMuch of the energy from burning fossil fuels to generate electricity in the U.S. is wasted as heat. Materials can convert a difference in temperature into an electrical voltage through the thermoelectric effect. This can be used in devices that help capture wasted heat. The most efficient thermoelectric materials are currently made from rare elements. Advanced plastics made from abundant carbon can also be tailored to conduct electricity and also have a thermoelectric effect. This project, funded by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, develops methods to understand and optimize the thermoelectric properties of plastics by controlling their electrical conductivity and the voltage generated by differences in temperature. The researchers create new materials that could be used to capture waste heat or integrated with common electronic devices for energy harvesting from the environment. This research is carried out by graduate students who gain skills in analyzing the properties of plastics and how to develop new materials. The training prepares graduate student researchers in multidisciplinary science for future careers in the U.S. workforce. These students also help to engage a diverse population in the benefits of research through outreach activities in local public schools. The broader public is engaged through partnerships with programs focused on science and engineering design projects for children.TECHNICAL SUMMARYOrganic thermoelectric materials present an opportunity to develop new means of controlling the conversion of electrical and thermal energy. New methods to control the thermoelectric properties of semiconducting polymers through processing, theory, and development of new electrical doping methods are being investigated in the project, which is funded by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF. Because the properties of semiconducting polymers are strongly dependent on processing methods, electrical doping methods that allow fixed morphologies of semiconducting polymers are studied to provide insight into the thermopower in disordered materials. Models for determining the changes in the electronic density of states upon doping are investigated using temperature-dependent measurements of thermopower and electrical conductivity. The interplay between crystallinity and electrical conductivity is studied to determine the evolution of the electronic structure upon doping. The properties of bulk polymers and controlled methods for doping them that leverage chemical activation in the solid state are also investigated. The resulting microstructures of materials are studied using advanced synchrotron X-ray scattering techniques and by spectroscopic methods. The impact on thermal conductivity by electrical doping is examined to determine if processing methods that improve electrical conductivity also increase the thermal conductivity. This research is carried out by graduate students who gain skills in analyzing the properties of plastics and how to develop new materials. The training prepares graduate student researchers in multidisciplinary science for future careers in the U.S. workforce. These students also help to engage a diverse population in the benefits of research through outreach activities in local public schools. The broader public is engaged through partnerships with programs focused on science and engineering design projects for children.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.