Improved thermoelectric performance in Cr-doped two-dimensional Bi2Te3

Abstract

Thermoelectric materials with high electrical conductivity and low thermal conductivity (e.g., Bi₂Te₃) can efficiently convert waste heat into electricity. However, despite favorable theoretical predictions, individual Bi₂Te₃ nanostructures such as two-dimensional (2D) nanoplates tend to underperform bulk Bi₂Te₃. We report a novel surface doping technique to synthesize highly n-type Bi₂Te₃ nanoplates using an external Cr coating followed by a thermal annealing process in a reducing atmosphere, as well as the mechanism by which this surface coating – only a few atoms or less in thickness – can observably impact the thermoelectric performance of 2D Bi₂Te₃. The Cr atoms act as n-type carrier donors by directly incorporating into the Bi₂Te₃ structure during thermal annealing, enhancing electrical conductivity by ∼ 70 % while increasing thermal conductivity by only ∼ 5 % at room temperature. Compared to the uncoated Bi₂Te₃ nanoplate, the Cr-doped Bi₂Te₃ nanoplate exhibits a doubled thermoelectric figure of merit (zT), which is still relatively low. Raman spectroscopy and chemical potential simulations further confirm that Cr atoms are incorporated into the Bi₂Te₃ structure.