Abstract
Thin films of p‐ and n‐type organic semiconductors for thermoelectrical (TE) applications are produced by doping of tetrathiotetracene (TTT). To obtain p‐type material TTT is doped with iodine during vacuum deposition of thin films or by postdeposition doping using controlled exposure to iodine vapors. Thermal codeposition in vacuum of TTT and tetracyanoquinodimethane (TCNQ) is used to prepare n‐type thin films. The attained thin films are characterized by measurements of the Seebeck coefficient and electrical conductivity. The Seebeck coefficient and conductivity can be varied by altering the doping level. p‐type TTT:iodide thin films with a power factor of 0.52 μW m−1 K−2, an electrical conductivity of 130 S m−1, and a Seebeck coefficient of 63 μV K−1 and n‐type TCNQ:TTT films with a power factor of 0.33 μW m−1 K−2, an electrical conductivity of 57 S m−1, and a Seebeck coefficient of −75 μV K−1 are produced. Engineered deposition of both p‐ and n‐type thermoelectric conducting elements on the same substrate is demonstrated. A proof of concept prototype of planar thin film TE generator based on a single p–n couple from the organic materials is built and its power generation is characterized.
Highlights
Growth in global energy consumption is becoming unsustainable
If the exposure to iodine vapors is ended before the conductivity starts to drop down, and chamber vented with ambient air, thin film electrical conductivity typically increases by one order
We have demonstrated that by appropriate doping of low cost TTT it is possible to obtain TE active organic thin films of both p- and n-types
Summary
Growth in global energy consumption is becoming unsustainable. Improving efficiency in 1 energy usage has become a global megatrend within all industies but across the entirety of society. TE devices are reliable and compact in comparison to conventional heat engines, because they directly convert thermal to electrical power and vice versa without moving parts or working fluids Besides this thermoelectric generators (TEGs) have other advantages such as: cleanness, operation without any noise and no discharge of any hazardous substance.[1] Presently the materials used for efficient TE devices are expensive, often not widely available and usually contain unsustainable or toxic elements such as Te, Pb and Se.[2,3,4,5,6] This has stimulated intensive studies seeking new sustainable thermoelectric materials. There is a pressing need for new TE materials, such as low cost sustainable organic materials, suitable for waste heat harvesting at lower temperature ranges by direct conversion in to electricity. Previous attention has focused on thin film TEGs prepared from inorganic materials or hybrid materials by combining electro-conductive polymers and TE active inorganic particles.[35,36,37,38,39,40] we aimed to study the TE properties of TTT based thin films, obtained by thermal evaporation in vacuum, and to demonstrate a practical all organic
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