Optimization of the thermoelectric figure of merit in the conducting polymer poly(3,4-ethylenedioxythiophene)

Abstract

Thermoelectric generators (TEGs) transform a heat flow into electricity. Thermoelectric materials are being investigated for electricity production from waste heat (co-generation) and natural heat sources. For temperatures below 200 °C, the best commercially available inorganic semiconductors are bismuth telluride (Bi(2)Te(3))-based alloys, which possess a figure of merit ZT close to one. Most of the recently discovered thermoelectric materials with ZT>2 exhibit one common property, namely their low lattice thermal conductivities. Nevertheless, a high ZT value is not enough to create a viable technology platform for energy harvesting. To generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs. This requires thermoelectric materials that are readily synthesized, air stable, environmentally friendly and solution processable to create patterns on large areas. Here we show that conducting polymers might be capable of meeting these demands. The accurate control of the oxidation level in poly(3,4-ethylenedioxythiophene) (PEDOT) combined with its low intrinsic thermal conductivity (λ=0.37 W m(-1) K(-1)) yields a ZT=0.25 at room temperature that approaches the values required for efficient devices.

Photoinduced p‐ to n‐type Switching in Thermoelectric Polymer‐Carbon Nanotube Composites

“…[ 7,8 ] The fully lowcost potential relies, however, on achieving realistic performance while keeping the processing schemes simple, including patterning of different materials. [9][10][11] Organic thermoelectric generators offer the potential for a cost-effective technology to harvest low temperature waste heat. [ 8,11 ] While it is possible to build complete thermoelectric modules from a single type of thermoelectric material (either p-or n-type) and interconnect them with a regular conductor, only half of the legs will actually generate a thermovoltage.…”

“…[9][10][11] Organic thermoelectric generators offer the potential for a cost-effective technology to harvest low temperature waste heat. [ 8,11 ] While it is possible to build complete thermoelectric modules from a single type of thermoelectric material (either p-or n-type) and interconnect them with a regular conductor, only half of the legs will actually generate a thermovoltage. A more effi cient device combines p-and complementary n-type materials by electrically connecting them in series and thermally in parallel in an alternating fashion.…”

“…[ 12,13 ] Interestingly, the thermal conductivity of bulk polymers as well as conjugated macromolecules can be tuned by controlling molecular orientation. [14][15][16] In order to increase the modest electrical conductivity of polymers, a number of strategies have been proposed, including careful doping, [ 4,11,[17][18][19][20][21] making composites of polymers with conductive fi llers such as CNTs, [22][23][24] or fabricating multilayer composite A broad range of organic electronic applications rely on the availability of both p-and n-type organic semiconductors, and the possibility to deposit them as sequential layers or to form spatial patterns. Examples include transport layers in diodes (OLEDs, photovoltaics, etc.…”

Organic π-type thermoelectric module supported by photolithographic mold: a working hypothesis of sticky thermoelectric materials

“…In this study, we first optimize p-type and n-type TE materials based on the common organic materials, poly(3,4-ethylenedioxy thiophene) polystyrene sulfonate (PEDOT:PSS) and tetrathiafulvalene 7,7,8,8-tetracyanoquinodimethane salt (TTF-TCNQ) [15,16]. Although dedoping of PSS yielded ZT  = 0.42 in PEDOT:PSS [9], the demonstrated process cannot be implemented as an economic mass-production process because the spin-cast PEDOT:PSS must be immersed once in ethylene glycol for 1 h for every 20–125 nm deposition; the organic TE legs need at least 20 µm thickness to maintain the internal Δ T .…”

“…Therefore, we also examine dedoping of PSS using an anion absorbent, where the anionic sulfonic group of PSS should be captured in a mixture solution with the anion absorbent before being injected into the photolithographic mold. Related to the material optimization, we also report detailed preparatory conditions of the n-type TE leg material because the previous reports only describe the mixing ratio of TTF-TCNQ and polyvinylchloride (PVC) [15,16]. When a single π-unit reaches 3 mV, the designed module can reach 250 mV to drive electric devices with a commercially available booster circuit designed for energy harvesting usage.…”