Enhanced Thermoelectric Performance of p-Type Sb/Ag Co-Doped Bi ₂ Te ₂ Se and n-Type W/Cl Co-Doped Bi ₂ Te 2.7 Se 0.3 and Module Configuration Optimization

This study reaffirmed the high effectiveness of co-doping strategies in enhancing the figure of merit zT of both p- and n-type Bi 2 Te 3 -based materials. Sb/Ag and W/Cl co-doping simultaneously optimized the carrier concentration and suppressed the lattice thermal conductivity in p-type Bi 2 Te 2 Se and n-type Bi 2 Te 2.7 Se 0.3, respectively. The effectiveness of Sb/Ag and W/Cl co-doping was supported by the density of states obtained from first-principles electronic structure calculations using, for each co-doped composition, a single large supercell containing all relevant dopants. Moreover, it was demonstrated that the thermoelectric properties of Bi 2 Te 3 -based systems were highly sensitive to synthesis conditions. For example, the sign of the Seebeck coefficient of the samples prepared in this study was opposite to that reported previously. A zT of ∼0.94 at 400 K was obtained for p-type BiSb 0.95 Ag 0.05 Te 2 Se, while a zT of ∼0.92 at 325 K was obtained for n-type Bi 1.9995 W 0.0005 Te 2.697 Se 0.3 Cl 0.003 . The p-type BiSb 0.95 Ag 0.05 Te 2 Se and the n-type Bi 1.9995 W 0.0005 Te 2.697 Se 0.3 Cl 0.003, both possessing high power factors and high zT values, exhibited slightly different electrical and thermal transport properties ( ρ n κ p / ρ p κ n ∼ 0.8, where ρ and κ represent the electrical resistivity and thermal conductivity of respective materials). However, the finite element simulation confirmed that a module composed of these materials exhibited high output power and high conversion efficiency, even when the p- and n-type legs were designed with identical geometries, such as cross-sectional area and height.