Intriguing substitution of conducting layer triggered enhancement of thermoelectric performance in misfit-layered (SnS)1.2(TiS2)2

We have systematically investigated the thermoelectric properties of misfit-layered chalcogenide (SnS)1.2(TiS2)2. Surprisingly, an unexpected Cu and Co substitution in the conducting TiS2 layer, acceptor dopant, can induce an exotic enhancement of thermoelectric performance. In particular, the value of dimensionless figure of merit ZT has increased by 33.3% and up to 0.42 at 720 K for Cu-substituted (SnS)1.2(Cu0.02Ti0.98S2)2. The present findings demonstrate that large effective mass and low carrier concentration are responsible for the emergence of large Seebeck coefficient and high power factor. Furthermore, the enhanced disorder effect due to the substitution accounts for the decrease of electronic thermal conductivity, while the increased phonon scattering of interlayer between SnS and TiS2 layers leads to the reduction of phononic thermal conductivity. Consequently, the Cu- and Co-substituted (SnS)1.2(TiS2)2 could be considered as a promising candidate of thermoelectric materials.