Improvement of thermoelectric performance of Bi2Te2.7Se0.3via grain boundary engineering with melting KOH

Grain boundary engineering is considered an effective approach to improve the performance of thermoelectric materials. Herein, by introducing KOH into the grain boundary of Bi2Te2.7Se0.3 (BTS) via liquid phase sintering strategy, the thermoelectric performances are improved significantly. The melting KOH spreads over the grain boundaries during the high temperature sintering process, which could be used to optimize the carrier/phonon transport behavior. The maximum ZT reaches up to 0.97 for the sample incorporated with 0.5% Wt of KOH at 425 K, which achieves 30% improvement over the pure BTS. The homogeneous distribution of KOH layer on the grain boundaries forms efficient potential barrier scattering, which increases power factor and reduces thermal conductivity simultaneously. Particularly, it is found that the maximum ZT can be tuned gradually in the temperature range from 450 K to 375 K by tuning the weight percent of KOH, demonstrating a possibility in adjusting the thermoelectric properties of BTS using a relatively simple method.