Bi₂Te₃ single crystals with high room-temperature thermoelectric performance enhanced by manipulating point defects based on first-principles calculation

Abstract

Intrinsic Bi₂Te₃ is a representative thermoelectric (TE) material with high performance at low temperature, which enables applications for electronic cooling. However, antisite defects easily form in p-type Bi₂Te₃, resulting in the difficulty of further property enhancement. In this work, the formation energy of native point defects in Bi₂Te₃ supercells and the electronic structure of Bi₂Te₃ primitive unit cell were calculated using first-principles. The antisite defect Bi_Te₁ has a lower formation energy (0.68 eV) under the Te-lack condition for p-type Bi₂Te₃. The effects of point defects on TE properties were investigated <i>via</i> a series of p-type Bi₂Te_3-<i>x</i> (<i>x</i> = 0, 0.02, 0.04, 0.06, 0.08) single crystals prepared by the temperature gradient growth method (TGGM). Apart from the increased power factor (PF_∥) which originates from the increased carrier concentration (<i>n</i> _∥) and <i>m</i>*, the thermal conductivity (<i>κ</i> _∥) was also cut down by the increased point defects. Benefitting from the high PF_∥ of 4.09 mW m^-1 K^-2 and the low <i>κ</i> _∥ of 1.77 W m^-1 K^-1, the highest <i>ZT</i> _∥ of 0.70 was obtained for <i>x</i> = 0.06 composition at 300 K, which is 30% higher than that (0.54) of the intrinsic Bi₂Te₃.