Broad Temperature Plateau for High Thermoelectric Properties of n-Type Bi₂Te_2.7Se_0.3 by 3D Printing-Driven Defect...

High-energy-conversion Bi₂Te₃-based thermoelectric generators (TEGs) are needed to ensure that the assembled material has a high value of average figure of merit (ZT_ave). However, the inferior ZT_ave of the n-type leg severely restricts the large-scale applications of Bi₂Te₃-based TEGs. In this study, we achieved and reported a high peak ZT (1.33) of three-dimensional (3D)-printing n-type Bi₂Te_2.7Se_0.3. In addition, a superior ZT_ave of 1.23 at a temperature ranging from 300 to 500 K was achieved. The high value of ZT_ave was obtained by synergistically optimizing the electronic- and phonon-transport properties using the 3D-printing-driven defect engineering. The nonequilibrium solidification mechanism facilitated the multiscale defects formed during the 3D-printed process. Among the defects formed, the nanotwins triggered the energy-filtering effect, thus enhancing the Seebeck coefficient at a temperature range of 300-500 K. The effective scattering of wide-frequency phonons by multiscale defects reduced the lattice thermal conductivity close to the theoretical minimum of ∼0.35 W m^-1 k^-1. Given the advantages of 3D printing in freeform device shapes, we assembled and measured bionic honeycomb-shaped single-leg TEGs, exhibiting a record-high energy conversion efficiency (10.2%). This work demonstrates the great potential of defect engineering driven by selective laser melting 3D-printing technology for the rational design of advanced n-type Bi₂Te_2.7Se_0.3 thermoelectric material.