Abstract With years of development, SnTe as a homologue of PbTe has shown great potential for thermoelectric applications in p‐type conduction, and the most successful strategy is typified by alloying for maximizing the valence band degeneracy. Among the known alloy agents, MnTe has been found to be one of the most effective enabling a band convergence for an enhancement in electronic performance of SnTe, yet its solubility of only ~15 at% unfortunately prevents a full optimization in the valence band structure. This work reveals that additional PbTe alloying not only promotes the MnTe solubility to locate the optimal valence band structure but also increases the overall substitutional defects in the material for a substantial reduction in lattice thermal conductivity. In addition, PbTe alloying simultaneously optimizes the carrier concentration due to the cation size effect. These features all enabled by such a solute manipulation synergistically lead to a very high thermoelectric figure of merit, zT of ~1.5 in SnTe with a 20 at% MnTe and a 30 at% PbTe alloying (Sn0.5Mn0.2Pb0.3Te), demonstrating the effectiveness of solute manipulation for advancing SnTe and similar thermoelectrics.
