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<p>Understanding heat transport in organic semiconductors is of fundamental and practical relevance. Therefore, we study the lattice thermal conductivities of a series of (oligo)acenes, where an increasing number of rings per molecule leads to a systematic increase of the crystals’ complexity. Temperature-dependent thermal conductivity experiments in these systems disagree with predictions based on the traditional Peierls–Boltzmann framework, which describes heat transport in terms of particle-like phonon propagation. We demonstrate that accounting for additional phonon-tunneling conduction mechanisms through the Wigner Transport Equation resolves this disagreement and quantitatively rationalizes experiments. The pronounced increase of tunneling transport with temperature explains several unusual experimental observations, such as a weak temperature dependence in naphthalene’s thermal conductivity and an essentially temperature-invariant conductivity in pentacene. While the anisotropic thermal conductivities within the acene planes are essentially material-independent, the tunneling contributions (and hence the total conductivities) significantly increase with molecular length in the molecular backbone direction. This, for pentacene results in a surprising minimum of the thermal conductivity at 300 K.</p>

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Heat transport in crystalline organic semiconductors: coexistence of phonon propagation and tunneling

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年2月14日

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  • Lukas Legenstein,
  • Lukas Reicht,
  • Sandro Wieser,
  • Michele Simoncelli,
  • Egbert Zojer

摘要

Understanding heat transport in organic semiconductors is of fundamental and practical relevance. Therefore, we study the lattice thermal conductivities of a series of (oligo)acenes, where an increasing number of rings per molecule leads to a systematic increase of the crystals’ complexity. Temperature-dependent thermal conductivity experiments in these systems disagree with predictions based on the traditional Peierls–Boltzmann framework, which describes heat transport in terms of particle-like phonon propagation. We demonstrate that accounting for additional phonon-tunneling conduction mechanisms through the Wigner Transport Equation resolves this disagreement and quantitatively rationalizes experiments. The pronounced increase of tunneling transport with temperature explains several unusual experimental observations, such as a weak temperature dependence in naphthalene’s thermal conductivity and an essentially temperature-invariant conductivity in pentacene. While the anisotropic thermal conductivities within the acene planes are essentially material-independent, the tunneling contributions (and hence the total conductivities) significantly increase with molecular length in the molecular backbone direction. This, for pentacene results in a surprising minimum of the thermal conductivity at 300 K.