Tailoring thermoelectric performance of n-type Bi2Te3 through defect engineering and conduction band convergence

Bi2Te3, an archetypical tetradymite, is recognised as a thermoelectric (TE) material of potential application around room temperature. However, large energy gap (Delta E-c) between the light and heavy conduction bands results in inferior TE performance in pristine bulk n-type Bi2Te3. Herein, we propose enhancement in TE performance of pristine n-type Bi2Te3 through purposefully manipulating defect profile and conduction band convergence mechanism. Two n-type Bi2Te3 samples, S1 and S2, are prepared by melting method under different synthesis condition. The structural as well as microstructural evidence of the samples are obtained through powder x-ray diffraction and transmission electron microscopic study. Optothermal Raman spectroscopy is utilized for comprehensive study of temperature dependent phonon vibrational modes and total thermal conductivity (kappa) of the samples which further validates the experimentally measured thermal conductivity. The Seebeck coefficient value is significantly increased from 235 mu VK-1 (sample S1) to 310 mu VK-1 (sample S2). This is further justified by conduction band convergence, where Delta E-c is reduced from 0.10 eV to 0.05 eV, respectively. To verify the band convergence, the double band Pisarenko model is employed. Large power factor (PF) of 2190 mu Wm(-1)K(-2) and lower kappa value leading to ZT of 0.56 at 300 K is gained in S2. The obtained PF and ZT value are among the highest values reported for pristine n-type bulk Bi2Te3. In addition, appreciable value of TE quality factor and compatibility factor (2.7 V-1) at room temperature are also achieved, indicating the usefulness of the material in TE module.