Manipulation of Band Structure and Interstitial Defects for Improving Thermoelectric SnTe

Many efforts are recently devoted on improving thermoelectric SnTe as an environmentfriendly alternative to conventional PbTe and successful approaches include valence band convergence, nanostructuring, and substantial/interstitial defects. Among these strategies, alloying SnTe with MnTe enables the most effective reduction in the valence band offset (between L and Sigma) for a convergence due to its high solubility of approximate to 15%, yet there is no indication that the solubility of MnTe is high enough for fully optimizing the valence band structure and thus for maximizing the electronic performance. Here, a strategy is shown to increase the MnTe solubility up to approximate to 25% by alloying with 5% GeTe, which successfully locates the composition (20% MnTe) to optimize the valence band structure by converging a more degenerated (as compared with band L) and Sigma valence bands. Through a further alloying with Cu2Te, the resultant Cu-interstitial defects enable a sufficient reduction in lattice thermal conductivity to its amorphous limit (0.4 W m(-1) K-1). These electronic and thermal effects successfully realize a record-high thermoelectric figure of merit, zT of 1.8, strongly competing with that of PbTe. This work demonstrates the validity of band manipulation and interstitial defects for realizing extraordinary thermoelectric performance in SnTe.