Thermoelectric materials are materials which can be used to convert thermal energy directly to electricity. The performance of a thermoelectric material is measured by the "figure of merit", termed ZT. There has been much research into increasing thermoelectric materials, figure of merit, however, progress in this area has been slow and most of the researched thermoelectric materials up to now are suffering from either high fabrication cost, usage of rare earth or toxic elements, or poor mechanical properties. Organic thermoelectric materials (OTEs) have recently attracted attention for low temperature applications (< 300K), especially cooling purposes, as they are flexible, low-cost and abundant, and low-cost fabrication methods for synthesizing them exist. However, the ZT of the state-of-the-art OTEs is significantly lower than the ZT of their inorganic counterparts. In fact, there are only few candidates for low temperature thermoelectric devices even among inorganic materials. In the case of inorganic thermoelectric materials, the limiting factor in improving ZT is the electron mobility. This work will allow for the fabrication of high-ZT thermoelectric materials by addressing the challenges in mobility enhancement. This will be done by combining the two classes of materials (organic and inorganic), using a fabrication scheme in which high-mobility inorganic nanowires are embedded inside organic compounds. The researchers are a multidisciplinary team with complementary expertise and with common interest in the thermoelectric field. Graduate and Undergraduate Students involved in this project therefore will benefit largely from the multidisciplinary nature of the work.
This work is applying new doping schemes (3D modulation-doping and field-effect doping) to hybrid organic-inorganic materials and to simulate, design, fabricate and characterize a new class of low temperature thermoelectric nanocomposites. The two-phase material uses the organic phase (e.g. conjugated-polymer or organic molecules) as a source of electrons and the inorganic semiconducting phase (e.g. Si nanowires) as the electron transport channel with high mobility. The key is to use the modulation-doping scheme to favor carrier transfer from the source of carriers (e.g. conjugated-polymer) to the high mobility inorganic semiconducting phase (inorganic nanowires) and optimize the carrier concentration to design a high Z hybrid thermoelectric material. A large class of semiconducting nanostructures (e.g. Si, CdTe, Bi, and PbTe nanowires and holely structures) combined with conjugated polymers (e.g., chemically-modified PEDOT and low bandgap polymers) and organic molecules (specifically charged chemical species attached to molecules such as CF3- substituted styrene molecules) will be simulated, synthesized and optimized to identify new hybrid materials with a potentially high ZT.
