Thermoelectric materials capable of converting waste heat into electrical energy have gained significant attention for energy recovery applications. Among these, chalcogenide-based nanomaterials, particularly lead telluride (PbTe) and tin selenide (SnSe), exhibit exceptional thermoelectric performance due to their unique electronic and phonon transport properties. These materials achieve high thermoelectric efficiency through a combination of anharmonic lattice dynamics, optimized doping strategies, and nanostructuring approaches that selectively scatter phonons while maintaining electronic conductivity.

Anharmonic lattice dynamics play a crucial role in the low thermal conductivity observed in chalcogenides. In PbTe and SnSe, the bonding asymmetry between heavy cations (Pb, Sn) and lighter chalcogens (Te, Se) leads to strong anharmonic vibrations. These vibrations suppress heat-carrying phonons without significantly affecting charge carrier mobility. SnSe, in particular, demonstrates an ultralow thermal conductivity of less than 0.5 W/m·K along certain crystallographic directions due to its highly anharmonic lattice. The intrinsic anharmonicity in these materials reduces the need for extensive extrinsic phonon scattering mechanisms, making them ideal for thermoelectric applications.

Solution-phase synthesis has emerged as a scalable and tunable method for producing high-quality chalcogenide thermoelectric nanomaterials. Colloidal approaches enable precise control over particle size, shape, and composition, which are critical for optimizing thermoelectric properties. For PbTe, hot-injection methods using precursors such as lead oleate and trioctylphosphine telluride yield monodisperse nanoparticles with diameters between 5 and 20 nm. Similarly, SnSe nanostructures can be synthesized via solvothermal routes using tin chloride and selenourea, producing anisotropic nanoplates that enhance phonon scattering. These solution-processed nanomaterials can be consolidated into bulk pellets through spark plasma sintering or hot pressing while preserving their nanostructured features.

Resonant doping is another key strategy for enhancing the thermoelectric performance of chalcogenides. By introducing dopants that create resonant energy levels near the Fermi level, the Seebeck coefficient can be significantly increased without degrading electrical conductivity. In PbTe, doping with elements such as sodium or thallium creates resonant states that enhance the density of states near the valence band edge, leading to power factor improvements exceeding 20 μW/cm·K². For SnSe, strategic doping with alkali metals like sodium or potassium optimizes carrier concentration while minimizing ionized impurity scattering. The interplay between resonant doping and intrinsic defects in these materials allows for fine-tuning of electronic transport properties.

Superlattice nanostructures further enhance thermoelectric efficiency by introducing periodic interfaces that selectively scatter phonons. In PbTe-based systems, alternating layers of PbTe and Sb₂Te₃ create coherent interfaces that disrupt phonon propagation while maintaining electron mobility. These superlattices reduce lattice thermal conductivity to values as low as 0.3 W/m·K, significantly below the bulk material limit. Similarly, SnSe-SnS superlattices exploit mass contrast and interface scattering to achieve comparable reductions in thermal conductivity. The periodicity and interface quality in these nanostructures are critical for maximizing phonon scattering without introducing excessive carrier recombination sites.

Automotive waste heat recovery represents a promising application for chalcogenide thermoelectric nanomaterials. Internal combustion engines waste approximately 60% of their energy as heat, primarily through exhaust gases and coolant systems. Thermoelectric modules incorporating PbTe or SnSe nanomaterials can convert this waste heat into usable electricity, improving overall vehicle efficiency. Prototype systems have demonstrated power outputs exceeding 500 W under realistic exhaust conditions, with conversion efficiencies approaching 10% for temperature gradients around 500°C. The mechanical robustness and thermal stability of these materials make them suitable for integration into automotive exhaust systems, where they operate under cyclic thermal and mechanical stresses.

The development of chalcogenide thermoelectric nanomaterials continues to advance through interdisciplinary research in materials synthesis, defect engineering, and device integration. Future efforts will likely focus on optimizing scalable synthesis techniques, further reducing thermal conductivity through hierarchical nanostructuring, and improving the stability of these materials under operational conditions. As the demand for energy-efficient technologies grows, chalcogenide-based thermoelectrics are poised to play a critical role in harnessing waste heat across industrial and automotive applications.