Interstitial Defects Improving Thermoelectric SnTe in Addition to Band Convergence

SnTe, as a top Pb-free alternative to PbTe, attracts extensive attention for thermoelectric applications. For thermoelectric performance enhancement, successful electronic strategies are typified by band convergence and resonant doping, while effective thermal strategies include nanostructuring and, recently, interstitial defects. This work demonstrates that phonon scattering by interstitial defects, as a nearly immune strategy integratable to band convergence, independently reduces the lattice thermal conductivity to the amorphous limit. This leads to a zT as high as 1.4 in Sn-1_yMgyTe(CuzTe)(x') where Cu2Te acts as the source of interstitial defects while MgTe converges the valence bands. Evolutionarily, either Cu2Te or MgTe enables a similar to 100% zT-enhancement as compared with that of pristine SnTe, while an overall similar to 200% enhancement is successfully realized when both exist. This work not only improves SnTe as an eco-friendly alterative to thermoelecric PbTe but also demonstrates an approach potentially applicable for improving thermoelectrics.