Tuning the Saturated Vapor Pressure of Solvothermal Synthesis to Boost the Thermoelectric Performance of Pristine Bi₂Te₃ Polycrystals by Anisotropy Strengthening

Bi₂Te₃ is one of the most promising thermoelectric materials that target near-room-temperature applications due to its high thermoelectric potential at these temperatures. In this work, we report a new route to significantly improve the thermoelectric performance of pristine Bi₂Te₃ polycrystals. We design the mixed solutions composed of H₂O and ethylene glycol (EG) as novel solvents to solvothermally synthesize Bi₂Te₃ crystalline microplates. It is found that the addition of H₂O can boost the saturated vapor pressure of the mixed solutions during the solvothermal synthesis and significantly drive the crystal growth of Bi₂Te₃ microplates along their in-plane directions due to the tuning of kinetic conditions. Such a unique route strengthens the anisotropy of the bulk materials sintered from these microplates, leading to improved carrier mobility of >170 cm² V^-1 s^-1 and in turn a high electrical conductivity of >1400 S cm^-1 at room temperature. Combined with a high absolute Seebeck coefficient of >140 μV K^-1, a competitively high power factor of ∼30 μW cm^-1 K^-2 can be achieved in the solvothermally synthesized samples. Besides, compared with the bulk material sintered from commercial Bi₂Te₃ powders with a figure of merit of 0.2 at 369 K, the figure of merit of the bulk material developed in this work is significantly improved by ∼167% (0.56), indicating great potential for practical applications.