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

Abstract

Polycrystalline SnSe has been widely explored due to its relatively low thermal conductivity. Yet its thermoelectric performance is limited due to the poor electrical conductivity. In this work, the polycrystalline SnSe alloyed with different content of CuAgSe were fabricated by high-energy balling and melting method, combined with spark plasma sintering. It is revealed that substitution of Ag and Cu on Sn sites would actually enhance the electrical conductivity, especially under Sndeficient circumstance where the formation energy of AgSn is lowered. While there were excessive addition of CuAgSe, the hole carrier concentration was limited due to the formation of Agi, which plays a role as electron donor. Additionally, partial Ag and Cu would fill the Sn vacancies, slight improving the hall mobility and density of states effective mass. With increased electrical conductivity and maintained Seebeck coefficient, the Sn0.99Se alloyed with 0.75%CuAgSe attains a maximum power factor of 6.40 µW cm−1 K−2 at 847 K, and the ultimate highest zT value reaches 0.97 at 847 K combined with marginally decreased thermal conductivity, exhibiting prominent improvement compared to that of the pure SnSe. The present work opens up a new perspective for optimizing thermoelectric performance of SnSe compounds with the strategy of tuning the content of Sn and alloying CuAgSe.