Thermoelectric performance of organic conductors

Abstract

Organic polymers such as poly(ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) have attracted attention as thermoelectric materials, but charge-transfer complexes have not been explored sufficiently though these materials show very high conductivity and even superconductivity. Here, the power factors of representative organic metals and superconductors are estimated down to low temperatures. Several metallic conductors show power factors comparable to that of PEDOT:PSS (3 μW cm⁻¹ K⁻²), when the metallic conductivity is maintained down to low temperatures. In particular, Cu(DMDCNQI)₂, where DMDCNQI is dimethyldicyanoquinonediimine, exhibits a power factor as large as 95 μW cm⁻¹ K⁻² and a Peltier conductivity of 3.7 A cm⁻¹ K⁻¹ at around 36 K, which are comparable to those of conventional inorganic thermoelectric materials. Since this is attributed to the participation of the Cu flat band and the resulting three-dimensional energy band, the use of metal complexes is a promising strategy to explore high-performance thermoelectric materials. Thermoelectric power has been evaluated from the band structure, but conductivity anisotropy is calculated, and the relaxation time is estimated by the combined use of the observed conductivity.