Large-area 2D bismuth antimonide with enhanced thermoelectric properties via multiscale electron-phonon decoupling

It is a challenge to obtain high thermoelectric efficiency owing to the conflicting parameters of the materials that are required. In this work, the composition-adjustable 2D bismuth antimonide (Bi_100-Sb) is synthesized using an e-beam evaporation system with homemade targets. Engineering multiscale defects is done to optimize the thermoelectric performance in the compound. Sb alloying introduces atomic defects, lattice distortion and increased grain boundary. They drastically decrease the thermal conductivity, with an ultralow value of ∼0.23 W m^-1 K^-1 obtained for the composition with x = 18. It is noticed that the atomic and nanoscale defects do not deteriorate the electrical conductivity (10⁵ S m^-1), and the value is even comparable to the bulk counterpart over a wide composition range (0 ≤ x ≤ 35). Annealing induces pore structure with microscale defects, which increase the Seebeck coefficient by 84% due to the energy barrier. The resultant ZT of 0.13 is enhanced by 420% in the annealed Bi₈₂Sb₁₈ when compared with the as-grown Bi. This work demonstrates a cost-effective and controllable way to decouple electrons and phonons in the thermoelectric field.