Room-Temperature Thermoelectric Performance of n-Type Multiphase Pseudobinary Bi 2 Te 3 -Bi 2 S 3 Compounds: Synergic Effects of Phonon Scattering and Energy Filtering.

Bismuth telluride-based alloys possess the highest efficiencies for the low-temperature-range (<500 K) applications among thermoelectric materials. Despite significant advances in the efficiency of p-type Bi2 Te3 -based materials through engineering the electronic band structure by convergence of multiple bands, the n - type pair still suffers from poor efficiency due to a lower number of electron pockets near the conduction band edge than the valence band. To overcome the persistent low efficiency of n-type Bi2 Te3 -based materials, we have fabricated multiphase pseudobinary Bi2 Te3 -Bi2 S3 compounds to take advantages of phonon scattering and energy filtering at interfaces, enhancing the efficiency of these materials. The energy barrier generated at the interface of the secondary phase of Bi14 Te13 S8 in the Bi2 Te3 matrix resulted in a higher Seebeck coefficient and consequently a higher power factor in multiphase compounds than the single-phase alloys. This effect was combined with low thermal conductivity achieved through phonon scattering at the interfaces of finely structured multiphase compounds and resulted in a relatively high thermoelectric figure of merit of ∼0.7 over the 300-550 K temperature range for the multiphase sample of n-type Bi2 Te2.75 S0.25 , double the efficiency of single-phase Bi2 Te3 . Our results inform an alternative alloy design to enhance the performance of thermoelectric materials.