Development of organic thermoelectric materials and devices for energy harvesting
Krishnakumar Menon, Akanksha
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Organic thermoelectrics have been limited by the lack of high performance n-type polymers and by low power outputs in existing prototype devices. To address these challenges, an n-type metallo-organic polymer was investigated and two new device architectures were proposed. Specifically, the synthesis and thermoelectric property optimization is presented for Poly(nickel-ethenetetrathiolate) or NiETT. By modifying reaction conditions and performing post-treatment by annealing, thermoelectric properties were enhanced 25x compared to literature reports for NiETT/PVDF composite films. This resulted in an n-type polymer film with a power factor over 20 µW/m-K2 that is stable in ambient conditions. As a parallel effort to developing materials, new device designs were developed that leverage the benefits of polymers, namely their low thermal conductivity and solution processability. First, a radial design based on characteristic thermal lengths for polymers is described. Analytical and numerical thermal models indicated a 10x improvement in power density for the radial thermoelectric generator (TEG) compared to conventional flat-plate TEGs. By using heat spreading, the device could operate under natural convection, thereby eliminating the need for active cooling, which reduces system cost. In the second design, a close-packed layout is presented that enables thin film TEGs with a high fill factor. By using fractal space filling curves as interconnect patterns, the TEG was divided into sub-modules for load matching to different applications, thereby eliminating the need for power conditioning circuits. These developments enable low cost thermoelectric applications for polymers such as waste heat recovery from pipes, and wearable electronics powered by body heat.