Synergistic effect approaching record-high figure of merit in the shear exfoliated n-type Bi₂O_2-2xTe_2xSe

Due to the nature of high stability and eco-friendliness, layered n-type Bi₂O₂Se-based thermoelectric materials have attracted extensive research interest. In order to reduce lattice thermal conductivity and enhance thermoelectric performance of Bi₂O₂Se-based thermoelectric materials, here, we introduced Te substitution at O site into Bi₂O_2-2xTe_2xSe prepared by a shear exfoliation method. The induced high-density nanosized Bi₂O₂Se grains and point defects can effectively scatter both mid and short-wavelength phonons, leading to a low lattice thermal conductivity of ~0.57 W m⁻¹ K⁻¹ at ~773 K. Furthermore, Se vacancies generated by the shear exfoliation induced a high carrier concentration approaching the optimized level, and in turn lead to relatively high electrical performance. The synergistic high electrical performance and low lattice thermal conductivity secured a record-high dimensionless figure of merit, zT, of ~0.69 at ~773 K. This study indicates that shear exfoliation method and Te substitution are promising methods to optimize the thermoelectric properties of Bi₂O₂Se-based thermoelectric materials.