High Thermoelectric Performance in Self-Synthesized NiSe/AgBiSe₂ Heterostructured Composites by Doping Ni in n-Type...

AgBiSe₂ is a promising intermediate-temperature n-type thermoelectric (TE) material. However, its performance enhancement has been constrained by limited modulation strategies. Here, the NiSe/AgBiSe₂ heterostructured composites were self-synthesized via Ni incorporation, realizing a ∼129% enhancement in figure of merit (ZT ∼1) at 783 K in Ag_0.985Ni_0.015BiSe₂. The results demonstrated a significant improvement (∼250%) in the electrical conductivity (σ) for Ag_0.94Ni_0.06BiSe₂, boosting the power factor PF by 98.6% to ∼4.9 µW cm^-1 K^-2 at 783 K. Simultaneously, ultralow lattice thermal conductivity (κ_L) was realized, for example, ∼0.17 W m^-1 K^-1 for Ag_0.985Ni_0.015BiSe₂ and even ∼0.13 W m^-1 K^-1 for Ag_0.955Ni_0.045BiSe₂ at 783 K, representing a ∼60% reduction. Systematic investigations indicate that the optimization of electrical transport properties stems from the substantial increase in n_H due to the combined contributions of selenium vacancy (V_Se), charge transfer, and Ni²⁺ dopant. What is more intriguing, the in situ precipitated NiSe second phase effectively decouples σ and the S, enhancing PF. Additionally, the κ_L suppression would be attributed to multiple phonon-scattering mechanisms introduced by multidimensional defects. Furthermore, a maximum theoretical TE conversion efficiency (𝜂_max) of ∼5.72% is attained. This work would offer a novel strategy for developing high-performance n-type AgBiSe₂-based TE materials by composite engineering.