Point Defect Engineering: Co-Doping Synergy Realizing Superior Performance in n-Type Bi₂ Te₃ Thermoelectric Materials

Bi₂ Te₃ has attracted great attention because of its excellent thermoelectric (TE) performance around room temperature. However, the TE property of the n-type Bi₂ Te₃ is still relatively low compared to the p-type counterpart, which seriously hinders its commercial application with a combination of the n-type and p-type materials. Herein, an effective process of Cl and W co-doping is employed into the n-type Bi₂ Te₃ materials to enhance its TE properties. The Bi_1.996 W_0.004 Te_2.476 Cl_0.024 Se_0.5 sample achieves a peak and average ZT over 1.3 and 1.2, respectively, at temperature range of 300-575 K. A 24-leg TE module of this n-type material and a home-made p-type Bi₂ Te₃ sample can produce a high efficiency over 6% at a temperature gradient of 235 K, which possesses a 71% improvement compared with a commercial Bi₂ Te₃ module. This high performance is ascribed to the effect of the Cl and W doping. This co-doping not only significantly increases the Grüneisen parameter but also successfully induces interstitial atoms in the van der Waals gap, which lead to a low lattice thermal conductivity (κ_l ) of 0.31W m^-1 K^-1 and a boosted charge transport. This finding represents an important step to promote the development of the n-type Bi₂ Te₃ materials.