Achieving superior thermoelectric performance in N-type SnS-based polycrystals by regulating donor dopability and phonon propagation

Abstract

Recent advancements in p-type SnS-based compounds have highlighted their potential for thermoelectric applications. Nevertheless, the thermoelectric properties of their n-type counterparts lag behind and have been seldom investigated to date, primarily owing to intrinsic Sn vacancies and limited donor dopability, which largely hinders the development of all SnS-based thermoelectric modules. Here, an effective doping strategy is proposed in n-type SnS-based polycrystals by incorporating PbSe along with a donor Br dopant. The electron concentration and power factor of PbSe alloyed compounds outperforms that of the matrix sample, being primarily credited to the improved dopability of Br dopant arising from the lower formation energy of Br dopant in the alloyed samples, as verified by first-principles calculations. Furthermore, the incorporation of PbSe remarkably diminishes the lattice thermal conductivity of the SnS-based materials, resulting from depressed phonon velocity, strengthened lattice anharmonicity and introduction of massive point defects. Consequently, an outstanding maximum zT value of ∼1.25 at 873 K, along with a decent average zT of ∼0.45 from 323 K to 873 K is attained in n-type 2.5 %PbBr₂-doped (SnS)_0.6(PbSe)_0.4 polycrystalline sample, representing record-high values in n-type SnS-based compounds. This research not only reveals that the optimal n-type SnS-based polycrystals are promising candidates for thermoelectric applications, but also offers insights into overcoming the doping bottleneck in thermoelectric materials.