IR spectroscopic-acoustical and surface tension studies of binary liquid mixtures at different temperatures T = (303.15, 308.15, 313.15 and 318.15) K

Strong Suppression of Thermal Conductivity in the Presence of Long Terminal Alkyl Chains in Low‐Disorder Molecular Semiconductors

“…The origin of these overestimations could be threefold: i) the predominance of the harmonic approximation in the expression of the potential energy (i.e., for bonds and angles) while anharmonic terms would yet better account for phonon–phonon interactions; ii) the occurrence of scattering processes at grain boundaries due to the polycrystalline nature of the organic thin films, as confirmed by the GIWAXS experiments; and/or iii) the presence of impurities that can strongly affect thermal transport by acting as phonon scattering centers. Another source of overestimation could arise from the absence of quantum corrections in our calculations; nevertheless, the Dulong–Petit model [ 50 ] can be considered as valid since the MD simulations are conducted at room temperature while the Debye temperature θ D of many OSCs rarely exceeds 100 K. [ 58,59 ] It is worth noting that Wang et al [ 23 ] reported an out‐of‐plane thermal conductivity κ out = 0.45 ± 0.06 W m –1 K –1 for a DNTT thin film with a thickness of 50 nm, as measured at room temperature by means of the differential 3ω method. By combining this value with the current experimental data, we obtain an anisotropy factor ≈ 2.5, which is very similar to the corresponding theoretical ratio ≈ 1.9, even though it must be borne in mind that the values of both in‐plane and out‐of‐plane thermal conductivities are overestimated by our theoretical calculations.…”