Thermal conductivity of benzothieno-benzothiophene derivatives at the nanoscale

Magatte Gueye (1) , Alexandre Vercouter (2) , Rémy Jouclas (3) , David Guérin (1, 4) , Vincent Lemaur (2) , Guillaume Schweicher (3) , Stéphane Lenfant (1, 5) , Aleandro Antidormi (6) , Yves Geerts (7, 3) , Claudio Melis (8) , Jerome Cornil (2) , Dominique Vuillaume (1, 5)

1 IEMN - Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520
2 UMONS - University of Mons [Belgium]
3 ULB - Université libre de Bruxelles
4 CMNF - IEMN - Centrale de Micro Nano Fabrication - IEMN
5 NCM - IEMN - Nanostructures, nanoComponents & Molecules - IEMN
6 ICN2 - Catalan Institute of Nanoscience and Nanotechnology
7 International Solvay Institutes for Physics and Chemistry [Brussels]
8 UniCa - Università degli Studi di Cagliari = University of Cagliari

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^-1 versus 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.

Mots clés: thermal conducHvity; scanning thermal microscopy (SThM); approach to equilibrium molecular dynamics (AEMD); organic semiconductor; organic thermoelectricity

Domaines: Matière Condensée [cond-mat]; Science des matériaux [cond-mat.mtrl-sci]; Physique [physics]; Sciences de l'ingénieur [physics]

Magatte Gueye, Alexandre Vercouter, Rémy Jouclas, David Guérin, Vincent Lemaur, et al.. Thermal conductivity of benzothieno-benzothiophene derivatives at the nanoscale. Nanoscale, 2021, 13 (6), pp.3800-3807. ⟨10.1039/D0NR08619C⟩. ⟨hal-03135025⟩