Air-Stable n-Type Organic Semiconductors for Thermoelectric Generators

摘要

Flexible thermoelectric generators, which convert waste heat into electricity, have received increasing attention as convenient and low-cost energy-harvesting devices. The performance of the thermoelectric materials is evaluated by the figure of merit ZT = S²σT/κ or the power factor PF = S²σ, where S, σ, T, and κ indicate the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity, respectively. Organic and organometallic semiconducting materials are particularly suitable for thermoelectric materials on account of their very low thermal conductivity, which affords significant advantages not only in realizing high ZT values, but also in generating a temperature gradient even in vertical direction relative to the thermoelectric films. Moreover, relatively large such films can be fabricated easily using a low-cost solution process. In the past decade, poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives have been intensively studied as solution-processable high-performance p-type materials. On the other hand, the development of n-type organic materials, which are equally important for efficient thermoelectric modules, has been hampered partially on account of their instability in air upon doping with an n-dopant.