Synergistic thermoelectric power factor increase in films incorporating tellurium and thiophene-based semiconductors
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esearch Letters
Synergistic thermoelectric power factor increase in films incorporating tellurium and thiophene-based semiconductors Jasmine Sinhaa), Robert M. Irelanda), Stephen J. Lee and Howard E. Katz*, Department of Materials Science and Engineering, Johns Hopkins University, 206 Maryland Hall, 3400 North Charles Street, Baltimore, Maryland 21218 *Address all correspondence to Howard E. Katz at [email protected] (Received 10 September 2012; accepted 12 March 2013)
Abstract Two thiophene-based semiconductors, a vapor-deposited small molecule and an amorphous polymer, as well as pentacene for comparison, show potential in enhancing the thermoelectric properties of tellurium (Te) nanowires. For vapor-deposited films, Te nanostructures form directly on glass substrates or organic semiconductor films. The resulting Te power factor (S2σ) was enhanced from 36 to 45 W/mK2 (56 for pentacene) because the bilayer provides an enhancement in Seebeck (S ) without compromising conductivity (σ). For solution deposited polymer blends, we obtained power factors from a Te nanowire network that alone would not have sufficient connectivity (up to 0.1 µW/mK2). While the organics are unoptimized, they are prototypical materials for further development.
There is growing and immediate interest in composites of inorganic particles and organic semiconducting materials for thermoelectric applications.[1–4] Such composites combine solution processing, mechanical flexibility, and potentially low thermal conductivity with useful power factors for energy capture from waste heat and local component cooling, potentially contributing to high values of the figure of merit ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electronic conductivity, T is the Kelvin temperature, and κ is the thermal conductivity.[5–7] Elemental tellurium (Te) is worthy of consideration for these purposes because of its well-defined composition, high charge carrier mobility, and submetallic charge carrier density.[8–10] The readiness with which Te forms nanostructures is favorable for homogeneous microscale mixing and possible reduction in thermal conductivity that is the main origin of inefficiencies in thermoelectric energy conversions. Recently, a collaboration at Lawrence Berkeley Laboratories demonstrated the dispersion of Te nanostructures in an aqueous solution of the conducting thiophene polymer poly (3,4-ethylenedioxythiophene) (PEDOT), and cast films of the combined materials to form composites with ZT of about 0.1.[11] The use of Te nanostructures in thermoelectrics was suggested earlier,[12] and the fundamental thermoelectric properties of elemental Te have appeared in the literature extending decades back.[13–16] In this communication we report that two thiophene-based semiconductors, one a vapor-deposited molecular solid and
a)
These authors contributed equally to this work.
the other an amorphous polymer (structures in Fig. 1), each show potential in enhancing the thermoelectric properties of Te nanowires, vapor deposited or mixed in, respectively. While
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