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. This work paves a new way and fills the gap of boosting the thermoelectric performance of pristine Bi2Te3.