Synergistic strategy via modulated energy filtering and hierarchical defects evolution for high performance GeTe thermoelectrics

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GeTe thermoelectric materials are very promising for sustainable waste-heat harvesting, while optimizations have been focusing on lowering lattice thermal conductivity or decreasing carrier concentration. As a long-pursued strategy to improve electronic transport properties, the full realization of effective energy filtering has been hindered by the mismatch between the energy barriers introduced and the intrinsic Fermi level of the matrix material. In this work, a synergistic strategy combining modulated energy filtering effect and hierarchical defect evolution engineering leads to ultrahigh performance GeTe-based thermoelectric materials. Very effective energy filtering is achieved by incorporating carbon fibers, which increases the overall energy of charge carriers. This greatly enhances Seebeck coefficient to over 230 μVK-1 with minor reduction in electrical conductivity which simultaneously decreases electronic thermal conductivity. Furthermore, the inclusion of carbon fibers modulates the microstructure of GeTe and facilitates the evolution of point defects to higher dimensional defects for broadband phonon scattering, greatly suppressing the lattice thermal conductivity to 0.3 Wm-1K-1. This strategy yields a prominent thermoelectric figure of merit ZTmax ∼ 2.3 and an exceptional quality factor Bmax ∼ 2.24 for Ge0.97Bi0.07Te with 0.9 wt% carbon fibers. This study demonstrates a promising strategy to modulate the convoluted thermoelectric properties for ultrahigh performance thermoelectric materials.