Strategies and Prospects for High-Performance Te-Free Thermoelectric Materials

Thermoelectric materials hold great potential for direct conversion of ubiquitous waste heat into electricity. However, their commercialization is hindered by low efficiency, reliance on rare and expensive Te, and limited stability under operating conditions. This review explores recent advances in novel strategies for achieving high thermoelectric performance and stability in Te-free inorganic bulk materials. First, we discuss diverse innovative techniques aimed at substantially enhancing electrical transport properties. These methods encompass strategies such as charge carrier engineering, band convergence, band inversion, valley anisotropy, multiband synglisis, and the incorporation of resonant levels or midgap states. Then we focus on strategies to reduce lattice thermal conductivity, including phonon scattering induced by multidimensional defects, off-center doping, resonance scattering, and lattice softening. Additionally, this review presents strategies for decoupling electron and phonon transport to enhance the thermoelectric performance of materials further. The strategies include interface engineering, crystal symmetry manipulation, high-entropy engineering and nanostructuring, high-pressure technology, and magnetically enhanced thermoelectrics. Moreover, we highlight novel strategies for improving the chemical and thermal stability of materials under operating conditions. Last, we discuss current controversies and challenges and suggest future directions for further research to improve the thermoelectric performance of Te-free bulk materials.