Phase Composition Manipulation and Twin Boundary Engineering Lead to Enhanced Thermoelectric Performance of Cu₂SnS₃

Cu2SnS3 (CTS), a typical ternary copper-based sulfide, is considered as a potential p-type thermoelectric (TE) material with the advantages of environmental friendliness and low cost, but its performance is limited by the high lattice thermal conductivity and electrical resistivity. Herein, we have successfully synthesized undoped and In-doped CTS nanoparticles with a pure tetragonal phase by the colloidal method. More interestingly, plenty of twin boundaries appear in all the samples sintered from the synthesized nanoparticles independent of composition. The twin boundaries can effectively reduce the lattice thermal conductivity, while the tetragonal phase is beneficial to meliorate the electrical performance of CTS. Consequently, the highest zT reaches 0.36 at 700 K for Cu2Sn0.85In0.15S3, which is enhanced by 17 times compared to that of the pristine CTS with mainly the monoclinic phase. The tunable phase and microstructure via the colloidal method provide useful guidance to promote the performance of eco-friendly TE sulfides.