Unravelling the need for balancing band convergence and resonant level in Sn_1-x-yIn_xMn_{yTe for high thermoelectric performance}

Sn1-delta Te is one of the few known chalcogenide semiconductors in which the thermoelectric performance can be significantly enhanced by manipulating its valence band structure through band convergence and resonant level (RL). However, these two mechanisms are usually considered as impacting the transport properties independently. Here, using In and Mn to induce both mechanisms in Sn1-x-yInxMnyTe, we demonstrate that these effects can be properly balanced to optimize the ZT values. As a result, an enhanced peak ZT value of 1.30 is achieved at 850 K in the (x, y) = (0.01, 0.06) sample. Electronic band structure calculations further evidence that the RL-induced broadening of the main valence band limits the benefit of band convergence, demonstrating the interplay of these two mechanisms. Our study clarifies the intertwined effects of band convergence and resonant level on the thermoelectric properties of Sn1-delta Te and provides general guidance for fully exploiting the benefits of both mechanisms in thermoelectric compounds.