Electron Delocalization Enhances the Thermoelectric Performance of Misfit Layer Compound (Sn_1–x Bi _x S)_1.2(TiS₂)₂

Abstract The misfit layer compound (SnS)1.2(TiS2)2 is a promising low-cost thermoelectric material because of its low thermal conductivity derived from superlattice-like structure. However, the strong covalent bonds within each constituent layer highly localized the electrons thereby it is highly challenging to optimize the power factor by doping or alloying. Here, we show Bi doping at the Sn site markedly breaks the covalent bonds networks and highly delocalizes the electrons. These results in a high charge carrier concentration and enhanced power factor throughout the whole temperature range. It is highly remarkably Bi doping also significantly reduces the thermal conductivity by suppressing the heat conduction carried by phonons, indicating it independently modulates phonon and charge transport properties. These effects collectively give rise to a maximum ZT of 0.3 at 720 K. In addition, we applied the single Kane band model and the Debye-Callaway model to clarify the electron and phonon transport mechanism in the misfit layer compound (SnS)1.2(TiS2)2.