Synergistic effect of Zn doping on thermoelectric properties to realize a high figure-of-merit and conversion efficiency in Bi2-xZnxTe3 based thermoelectric generators

In state-of-the-art bismuth telluride based thermoelectric devices, the n-type composition shows a lower figure-of-merit (zT) than the p-type counterpart due to intrinsic electrical anisotropy and bipolar conduction at elevated temperatures. Herein, we demonstrate a significant improvement in the zT values of n-type Bi2-xZnxTe3 (x = 0-0.3) materials through aliovalent Zn doping at the Bi-site in the rhombohedral Bi2Te3 structure. A simultaneous enhancement in the electrical conductivity (sigma) and Seebeck coefficient (alpha) with Zn doping is observed, which is attributed to the increased carrier concentration (n) and effective mass (m*), respectively. Concomitantly, a drastic enhancement in the power factor (alpha(2)sigma) from 2.4 mW m(-1) K-2 (x = 0) to 3.1 mW m(-1) K-2 (x = 0.2) at 430 K is achieved. In addition, the incorporation of Zn shows a significant reduction in the lattice and bipolar contributions to the total thermal conductivity (kappa), which drastically enhances the zT value to similar to 1.2 (x = 0.2) at 450 K. The achieved zT value is similar to 70% higher than that of the undoped Bi2Te3 sample. A unicouple module fabricated using n-type Bi1.8Zn0.2Te3 in combination with the compatible high zT p-type Bi0.5Sb1.495Cu0.005Te3 material shows a record-high conversion efficiency (eta) of similar to 8.1% at a temperature gradient (Delta T) of 224 K. The achieved eta is amongst the best-reported values till date in Bi2Te3 lab-scale thermoelectric power generators.