Tailoring 5s2 lone pair-antibonding orbital interaction by Zr-doping to realize ultrahigh power factor in thermoelectric GeTe

Abstract

Lead-free GeTe-based thermoelectric (TE) materials are most promising candidates to replace the environmentally harmful PbTe for TE application at middle temperature range, where high power factor (PF) is significantly important for high power generation if the cost of heat source is low enough. In this study, we report for the first time that the PF of GeTe can be greatly enhanced by tailoring the interaction between Te 5s2 lone pair and antibonding orbitals, which is induced by the hybridization of Zr 4d2 electrons with antibonding orbitals. As a result, the contribution of Ge 4s2 electrons to the valence band is promoted, leading to the band sharpening at the valence band maximum in rhombohedral phase, and simultaneous band sharpening at the valence band maximum and band flattening at the conduction band minimum in cubic phase. Lower band effective mass mb* effectively increases the carrier mobility to a very high value of ∼121 cm−2 V−1 s−1 (300 K), and the Seebeck coefficient is improved by the reduced detrimental effect of minority carrier in cubic phase, enhancing the maximum PF up to a record value of ∼5503 μW m−1 K−1. With the assistance of reduced thermal conductivity, a peak zT of ∼1.9 is achieved at 673 K, which is one of the highest values among single doped GeTe. This work provides a new guidance to enhance the TE performance of GeTe-based materials.