ZrNiSn-based half-Heusler compounds are promising thermoelectric materials for mid-to-high temperature power generation, but their widespread application is hindered by the costly reliance on hafnium for performance optimization. Herein, we present a cost-effective, Hf-free strategy that simultaneously enhances the power factor and figure of merit zT in n-type ZrNiSn via grain-boundary-engineered modulation doping. Metallic tungsten (W) nanoparticles are introduced as a secondary phase, where they spontaneously segregate to grain boundaries during consolidation. This microstructure creates a network of internal heterojunctions that perform two synergistic functions: charge injection from the low-work-function W elevates electrical conductivity, while interfacial energy-filtering barriers enhance the Seebeck coefficient. Consequently, the optimized composite achieves a peak power factor of 44 μW cm^-1 K^-2 and a zT of 0.76 at 910 K. Beyond intrinsic transport improvements, the practical viability of this material system is validated at the device level. When integrated into a thermoelectric unicouple, the material delivers an exceptional power density of 2.1 W cm^-2 and a conversion efficiency of 5.2% at a temperature difference of 307 K. Crucially, this approach eliminates expensive Hf, reducing material costs by over 95%. This work establishes grain‑boundary modulation doping as a cost‑effective route to enhance the power factor and zT of Hf‑free ZrNiSn, offering a pragmatic balance between performance and economic viability for mid‑temperature waste‑heat recovery.

The development of cost-effective and high-performance thermoelectric (TE) materials faces significant challenges, particularly in improving the properties of promising copper-based TE materials such as Cu₃SbSe₄, which are limited by their poor electrical conductivity. This study presents a detailed comparative analysis of three strategies to promote the electrical transport properties of Cu₃SbSe₄ through Sn doping: conventional Sn atomic doping, surface treatment with SnSe molecular complexes, and blending with SnSe nanocrystals to form nanocomposites, all followed by annealing and hot pressing under identical conditions. Our results reveal that a surface treatment using SnSe molecular complexes significantly enhances TE performance over atomic doping and nanocomposite formation, achieving a power factor of 1.1 mW·m⁻¹·K⁻² and a maximum dimensionless figure of merit zT value of 0.80 at 640 K, representing an excellent performance among Cu₃SbSe₄-based materials produced via solution-processing methods. This work highlights the effectiveness of surface engineering in optimizing the transport properties of nanostructured materials, demonstrating the versatility and cost-efficiency of solution-based technologies in the development of advanced nanostructured materials for application in the field of TE among others.