Rattling‐Induced Ultralow Thermal Conductivity in Black Phosphorus Through Organic‐Molecule Intercalation

Abstract Layered materials have attracted significant interest in the thermoelectric community due to their unique anisotropic crystal structures and exceptional planar electrical conductivity. However, their high intralayer lattice thermal conductivity presents an obstacle for thermoelectric applications. This work proposes a rattling‐scatter strategy to reduce intralayer lattice thermal conductivity through the intercalation of organic molecules, as demonstrated with ethylenediamine (EDA) intercalated into black phosphorus (BP). Theoretical calculations reveal that this mechanism significantly enhances lattice anharmonicity and reduces group velocity, achieving a more than one order of magnitude decrease in intralayer lattice thermal conductivity. Experimental results validate these findings, revealing a significantly reduced thermal conductivity of 0.13 Wm ⁻¹ K ⁻¹ at 300 K in BP/EDA composites, which is only 1.45% of that in polycrystalline BP. Additionally, EDA intercalation distorts the BP structure, causing conduction band convergence around the Fermi level and enhancing electrical performance. The BP/EDA is predicted to have an impressive zT value of 0.53 at 300 K, a staggering 19 fold increase over pristine BP. This study demonstrates that organic‐molecule intercalation effectively induces rattling motion, providing a promising strategy to suppress lattice thermal conductivity and improve thermoelectric performance in layered materials, thereby offering valuable insights for thermoelectric material design.