Phase-dependent microstructure modification leads to high thermoelectric performance in n-type layered SnSe2

Microstructure control is crucial for thermoelectrics since it is intimately related to the scattering mechanism of both electrons and phonons. Herein, we propose a new strategy to modify microstructure by phase regulation that simultaneously induces high carrier mobility and low lattice thermal conductivity . As demonstrated in layered SnSe 2 , the addition of Cu can induce a phase transition from space group P 3 ¯ m 1 to P 6 3 mc . Due to the enlarged formation energy of stacking faults in the later phase, the stacking fault density is greatly reduced after heat treatment that leads to an increased grain size . Accordingly, the carrier mobility of SnSe 1.97 Br 0.03 –3 % Cu sample is enhanced by 100 % at room temperature. Furthermore, the reduction of stacking fault density is accompanied by the formation of pores in the matrix, which results in low lattice thermal conductivity . As a result, a record peak zT of 1.13 for SnSe 2 -based materials is achieved at 773 K, and the attained ZT ave of 0.62 is a record-high value among n -type polycrystalline layered materials working in intermediate-to-high temperature region. This work provides a feasible strategy to decouple the electron and phonon transport in layered thermoelectric compounds by phase-dependent microstructure modification.