Researchers at Graz University of Technology (TU Graz), in collaboration with TU Vienna and the University of Cambridge, have uncovered the mechanisms behind heat transport in complex materials like organic semiconductors. Published in npj Computational Materials, their findings could revolutionize the design of materials with tailored thermal properties, impacting applications ranging from OLED displays to gas storage.
The study, led by Egbert Zojer’s team at TU Graz, focused on understanding how thermal energy moves through organic semiconductors—a question that had remained unanswered for decades. While previous research primarily explored charge transport, heat transport mechanisms had been largely overlooked. Using machine learning, the team identified a new mechanism called “tunnelling transport of phonons,” which complements the traditional particle-like transport model.
Phonons, energy packets associated with lattice vibrations, were previously thought to move similarly to gas particles. However, the new research reveals that the wave-like behavior of atomic vibrations also plays a crucial role, especially in materials with low thermal conductivity. This tunnelling effect becomes more significant as the size of the molecules in the material increases.
Lukas Legenstein, one of the study’s authors, explained, “Heat transport isn’t just about collisions of vibrational quanta. The tunnelling effect couples separate vibrational states, which explains why some organic semiconductors have unusually low temperature-dependent thermal conductivity.” This discovery allows scientists to design materials with specific thermal properties by manipulating molecular structures.
Egbert Zojer, the lead researcher, emphasized the importance of the findings: “For 40 years, scientists have studied charge transport in organic semiconductors, but heat transport was ignored. Now, we can precisely determine and understand heat transport, which is unparalleled.”
The breakthrough not only sheds light on heat transport in organic semiconductors but also opens new possibilities for designing materials with customized thermal properties. The team plans to apply these insights to metal-organic frameworks (MOFs), where heat transport is even more critical. This research could lead to innovations in energy-efficient materials, thermoelectric devices, and more.
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