Optimized thermoelectric properties of SnSe through the joint strategies of Sn-content fine-tuning and CuAgSe alloying

Polycrystalline SnSe has been widely explored due to its relatively low thermal conductivity. Yet its thermoelectric performance is limited due to its poor electrical conductivity. In this work, polycrystalline SnSe alloyed with different contents of CuAgSe were fabricated by a high-energy balling and melting method, combined with spark plasma sintering. It is revealed that substitution of Ag and Cu at Sn sites actually enhances the electrical conductivity, especially under Sn-deficient circumstances where the formation energy of Ag_Sn is lowered. When there was excessive addition of CuAgSe, the hole carrier concentration was reduced due to the formation of Ag_i, which acts as an electron donor. Additionally, partial substitution of Ag and Cu into the Sn vacancies slightly improves the Hall mobility and the density of states effective mass. With increased electrical conductivity while maintaining a stable Seebeck coefficient, the Sn_0.99Se sample alloyed with 0.75% CuAgSe attains a maximum power factor of 6.40 μW cm^-1 K^-2 at 847 K. In addition, a peak <i>zT</i> value of 0.97 at 847 K is achieved, combined with only a marginally decreased thermal conductivity, thereby exhibiting a prominent improvement over that of the pure SnSe sample. The present work opens up a new perspective for optimizing the thermoelectric performance of SnSe compounds with the strategy of tuning the content of Sn and alloying with CuAgSe.