Defect-tolerant electron and defect-sensitive phonon transport in quasi-2D conjugated coordination polymers.

Un, Hio-Ieng; Iwanowski, Kamil; Ferrer Orri, Jordi; Jacobs, Ian E; Fukui, Naoya; Cornil, David; Beljonne, David; Simoncelli, Michele et al. · Nat Commun · 2025

basic_science · Level V

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Abstract

Thermoelectric materials, enabling direct waste-heat to electricity conversion, need to be highly electrically conducting while simultaneously thermally insulating. This is fundamentally challenging since electrical and thermal conduction usually change in tandem. In quasi-two-dimensional conjugated coordination polymer films we discover an advantageous thermoelectric transport regime, in which charge transport is defect-tolerant but heat propagation is defect-sensitive; it imparts the ideal mix of antithetical properties-temperature-activated, exceptionally low lattice thermal conductivities of 0.2 W m<sup>-1</sup> K<sup>-1</sup> below Kittel's limit originating from small-amplitude, quasi-harmonic lattice dynamics with disorder-limited lifetimes and vibrational scattering length on the order of interatomic spacing, and high electrical conductivities up to 2000 S cm<sup>-1</sup> with metallic temperature dependence, notably in poorly crystalline structures with paracrystallinity >10%. These materials offer attractive properties, such as ease of processing and defect tolerance, for applications, that require fast charge, but slow heat transport.