Functionally separated electronic band engineering via multi-element doping plus high-density defects advances board-temperature-range thermoelectric performance in GeTe

Adopting functionally separated electronic band engineering strategy (resonance energy levels and band convergence) coupling the construction of high-density defects to weaken electron–phonon coupling optimizing thermoelectric performance in SnSe-In-Sb codoping GeTe in a broad temperature range. [Display omitted] •Resonant levels of In and band convergence of SnSe cooperate to optimize S.•Optimized symmetry and carrier concentration of Sb further lead to high S2σ.•High-density defects strongly suppress lattice thermal conductivity.•The ZTmax of ∼ 2.0 (653 K) and ZTave of ∼ 1.2 (303 K-803 K) is achieved.•A high Vickers microhardness of ∼ 234 Hv is achieved. GeTe has attracted widespread attention as an ideal mid-temperature thermoelectric (TE) material, but its peak performance within a narrow mid-temperature range limits the conversion efficiency improvement of future TE devices. Here, to achieve the overall enhancement of GeTe over a broad temperature range, especially near room temperature, we demonstrate the functionally separated electronic band engineering strategy (resonance energy levels and band convergence) coupling the construction of high-density defects by designing multi-element SnSe-In-Sb co-doping. Fundamentally, to distinguish the functions of selected elements, it was found that SnSe alloying mainly promotes the band convergence of GeTe in elevated temperatures, In doping can create the resonance energy level for enhancing the TE performance near room temperature, and Sb can optimize symmetry and the overall carrier concentration, thereby jointly improving the effective mass and Seebeck coefficient. Moreover, the construction of various phonon scattering centers including high-density Ge micro/nano-precipitates, van der Waals gaps, dislocations, and strong stress fields, strongly inhibits phonon transport. Benefiting from these synergistic effects, a peak ZT of ∼ 2.0 at 653 K, ZTave of ∼ 1.2 in the range from 303 to 803 K, and Vickers microhardness of ∼ 234 Hv are obtained in (Ge0.91In0.01Sb0.08Te)0.98(SnSe)0.02 sample. This study demonstrates a promising strategy to optimize thermoelectric performance by selectively co-doping functionally separated elements for developing high-performance TE materials.