Ultrahigh average zTrealized in polycrystalline SnSe0.95materials through Sn stabilizing and carrier modulation

The average zTdetermines the conversion efficiency, and the power factor plays an important role in average zTvalue. However, the inadequate electrical conductivity of SnSe materials seriously limits its application. Herein, the TaCl5-doped in polycrystalline SnSe0.95materials synthesized using the melting method and combined with spark plasma sintering technology achieves a zTvalue of 1.64 at 773 K and a record zTaveof 0.62 from 323 K to 773 K. The electrical conductivity increases due to the released electron carrier induced by effective TaCl5doping. According to the DFT calculation, the energy band of TaCl5-doped samples is narrowed, which can enhance the electron transport. Besides, the Seebeck coefficient is maintained at an elevated level as a result of the incorporation of the heavy element Ta. Due to the significantly enhanced electrical conductivity and maintained high Seebeck coefficient, the power factor reaches to 622 μW·m−1·K−2at 773 K for the SnSe0.95 + 1.75% (in mass) TaCl5sample, which is almost 21 times higher than that of the pristine sample. Simultaneously, a high average power factor value of 334 μW·m−1·K−2for the SnSe0.95 + 1.75% (in mass) TaCl5sample from 323 to 773 K was obtained. It is surprisingly found that the Ta element plays another important role to improve the stability of SnSe0.95by forming Ta2Sn3and removing the low melting point Sn, which usually existed in n-type SnSe samples, resulting in the decreased lattice thermal conductivity. A low lattice thermal conductivity value of 0.24 W·m−1·K−1was also obtained for the SnSe0.95 + 2.0% (in mass) TaCl5sample at 773 K due to the multiscale defects. Consequently, the SnSe0.95 + 2.0% (in mass) TaCl5sample obtains a peak zTvalue of 1.64 at 773 K and a record zTaveof 0.62 from 323 to 773 K, and the theoretically calculated conversion efficiency reaches 11.2%, it can be utilized for power generation and/or cooling at a broad temperature range. This strategy of introducing high-valence halides with heavy element can optimize the thermoelectric performance for other material systems.