  The search for thermoelectrics with higher figures of merit (ZT) will never
stop due to the demand of heat harvesting. Single layer transition metal
dichalcogenides (TMD), namely MX2 (where M is a transition metal and X is a
chalcogen) that have electronic band gaps are among the new materials that have
been the focus of such research. Here, we investigate the thermoelectric
transport properties of hybrid armchair-edged TMDs nanoribbons, by using the
nonequilibrium Green's function technique combined with the first principles
and molecular dynamics methods. We find a ZT as high as 7.4 in hybrid
MoS2/MoSe2 nanoribbons at 800K, creating a new record for ZT. Moreover, the
hybrid interfaces by substituting X atoms are more efficient than those by
substituting M atoms to tune the ZT. The origin of such a high ZT of hybrid
nanoribbons is the high density of the grain boundaries: the hybrid interfaces
decrease thermal conductance drastically without a large penalty to electronic
conductance.
