GeSb₄Te₇, a quasi-two-dimensional semiconductor, exhibits high potential in thermoelectric applications. Herein, efficacious Yb/In co-doping has been realized in the GeSb₄Te₇ single crystals prepared by the slow-cooling method to enhance their thermoelectric properties. DFT calculations demonstrate that the inherently low lattice thermal conductivity of GeSb₄Te₇ is associated with its low phonon group velocities and strong lattice anharmonicity. Yb doping at Ge sites significantly lowers the lattice thermal conductivity, primarily by promoting phonon scattering from point defects. Furthermore, In doping creates an impurity band, leading to a distortion in the density of states (DOS) near the Fermi level and contributing to enhanced Seebeck coefficient. Benefiting from enhanced electrical properties and decreased thermal conductivity, the zT of Yb/In co-doped samples is markedly improved: Ge_0.95Yb_0.02In_0.03Sb₄Te₇ single-crystal sample obtains a record peak zT (0.81) at 673 K and maintains an average zT (0.55) between 323 K and 773 K, signifying a rise of 62% and 83%, respectively, compared with the pristine GeSb₄Te₇. This study proposes a novel strategy to boost the thermoelectric properties of layered-structured GeSb₄Te₇ compounds.

Pseudo-binary layered compound IVVI-V₂VI₃ families show great promise for application in thermoelectrics. Herein, through introducing iodine in GeSb₂Te₄, several synergistic effects come into being and contribute to outstanding thermoelectric performance. The I^Te donor-like defects suppress the hole carrier concentration from 5.72 × 10²⁰ cm⁻³ to 2.80 × 10²⁰ cm⁻³. First-principles calculations reveal that iodine doping increases the band gap from 0.253 eV to 0.302 eV and contributes to valence band convergence. Seebeck coefficient value reaches up to 135.7 μV/K at 773 K, and the power factor values are entirely boosted in the whole temperature region, reaching a maximum value of 12.4 μW·cm⁻¹·K⁻² in GeSb₂Te_3.96I_0.04. Moreover, iodine doping simultaneously reduces the lattice and electronic thermal conductivity, leading to the greatly reduced total thermal conductivity from 2.89 W·m⁻¹·K⁻¹ in pristine sample to 0.89 W·m⁻¹·K⁻¹ in GeSb₂Te_3.84I_0.16 at 323 K. Finally, a maximum zT ~1.12 at 773 K and an average zT ~0.62 over 323–773 K are achieved in GeSb₂Te_3.88I_0.12. This work puts forward an effective strategy to synergistically optimize phonon and carrier transport properties of pseudo-binary compounds through halogen doping, which may be effective in other similar material systems.