While the charge transport properties of organic semiconductors have been extensively studied over the recent years, the field of organics-based thermoelectrics is still limited by a lack of experimental data on thermal transport and of understanding of the associated structure–property relationships. To fill this gap, a comprehensive experimental and theoretical investigation of the lattice thermal conductivity in polycrystalline thin films of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (Cn-DNTT-Cn with n = 0, 8) semiconductors is reported. Strikingly, thermal conductivity appears to be much more isotropic than charge transport, which is confined to the 2D molecular layers. A direct comparison between experimental measurements (3ω–Völklein method) and theoretical estimations (approach-to-equilibrium molecular dynamics (AEMD) method) indicates that the in-plane thermal conductivity is strongly reduced in the presence of the long terminal alkyl chains. This evolution can be rationalized by the strong localization of the intermolecular vibrational modes in C8-DNTT-C8 in comparison to unsubstituted DNTT cores, as evidenced by a vibrational mode analysis. Combined with the enhanced charge transport properties of alkylated DNTT systems, this opens the possibility to decouple electron and phonon transport in these materials, which provides great potential for enhancing the thermoelectric figure of merit ZT.

中文翻译：

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在低无序分子半导体中存在长末端烷基链时强烈抑制热导率

虽然近年来有机半导体的电荷传输特性得到了广泛的研究，但基于有机物的热电领域仍然受到缺乏热传输实验数据和对相关结构-性质关系理解的限制。为了填补这一空白，对萘并 [2,3-b:2',3'-f] 噻吩并 [3,2-b] 噻吩 (C n - DNTT-C n与n = 0, 8) 报告了半导体。引人注目的是，热导率似乎比电荷传输更具各向同性，电荷传输仅限于二维分子层。实验测量（3ω-Völklein 方法）和理论估计（接近平衡分子动力学 (AEMD) 方法）之间的直接比较表明，在长末端烷基链的存在下，面内热导率大大降低。与未取代的 DNTT 核相比，C8-DNTT-C8 中分子间振动模式的强定位可以使这种演变合理化，振动模式分析证明了这一点。结合烷基化 DNTT 系统增强的电荷传输特性，这开启了在这些材料中解耦电子和声子传输的可能性，ZT。