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

Bi 2 Te 3 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 Bi 2 Te 3 polycrystals. We design the mixed solutions composed of H 2 O and ethylene glycol (EG) as novel solvents to solvothermally synthesize Bi 2 Te 3 crystalline microplates. It is found that the addition of H 2 O can boost the saturated vapor pressure of the mixed solutions during the solvothermal synthesis and significantly drive the crystal growth of Bi 2 Te 3 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 cm 2 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 Bi 2 Te 3 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. This work paves a new way and fills the gap of boosting the thermoelectric performance of pristine Bi 2 Te 3 .