Progressive carrier density optimization contributes to enhanced thermoelectric performance in Bi(Te, Se) compound

Layered BiTe and BiSe compounds present promising n-type thermoelectric performance, but the intrinsic high carrier density limits ZT value near room temperature. In this work, thermoelectric performance in Bi(Te, Se) compound is significantly improved by progressively optimizing its carrier density. The room-temperature carrier density is reduced from ∼5.5 × 10²⁰ cm⁻³ in Bi_0.99Te to ∼2.21 × 10²⁰ cm⁻³ in Bi_0.92Sn_0.07Te_0.4Se_0.6-2%Cu, which can lead to obvious enhancement of Seebeck coefficient and power factor, and thus the room-temperature power factor increases from ∼4.17 μW cm⁻¹ K⁻² in Bi_0.99Te to ∼9.78 μW cm⁻¹ K⁻² in Bi_0.92Sn_0.07Te_0.4Se_0.6-2%Cu. Moreover, the largely suppressed total thermal conductivity in Bi_0.92Sn_0.07Te_0.4Se_0.6-2%Cu also benefit from lowered carrier density because of reduced electronic thermal conductivity, as well as intensified phonon scattering caused by imported point defects. Finally, a room-temperature ZT of ∼0.29 and a peak value of ∼0.41 at 373 K in Bi_0.92Sn_0.07Te_0.4Se_0.6-2%Cu are achieved successfully, which are ∼6 and ∼3 times higher than that in Bi_0.99Te, respectively.