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Thermal conductivity of benzothieno-benzothiophene derivatives at the nanoscale

par Gueye, Magatte N.;Vercouter, Alexandre;Jouclas, Remy ;Guérin, David;Lemaur, Vincent;Schweicher, Guillaume ;Lenfant, Stéphane;Antidormi, Aleandro;Geerts, Yves ;Melis, Claudio;Cornil, Jérôme;Vuillaume, Dominique
Référence Nanoscale, 13, page (3800-3807)
Publication Publié, 2021-02-04

Article révisé par les pairs

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Résumé :

We study by scanning thermal microscopy the nanoscale thermal conductance of films (40–400 nm thick) of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT-C8). We demonstrate that the out-of-plane thermal conductivity is significant along the interlayer direction, larger for BTBT (0.63 ± 0.12 W m−1 K−1) compared to C8-BTBT-C8 (0.25 ± 0.13 W m−1 K−1). These results are supported by molecular dynamics calculations (approach to equilibrium molecular dynamics method) performed on the corresponding molecular crystals. The calculations point to significant thermal conductivity (3D-like) values along the 3 crystalline directions, with anisotropy factors between the crystalline directions below 1.8 for BTBT and below 2.8 for C8-BTBT-C8, in deep contrast with the charge transport properties featuring a two-dimensional character for these materials. In agreement with the experiments, the calculations yield larger values in BTBT compared to C8-BTBT-C8 (0.6–1.3 W m−1 K−1versus 0.3–0.7 W m−1 K−1, respectively). The weak thickness dependence of the nanoscale thermal resistance is in agreement with a simple analytical model.