Significant Optimization of Electron-Phonon Transport of n-Type Bi2O2Se by Mechanical Manipulation of Se Vacancies via Shear Exfoliation.

Very recently, a novel layered oxyselenide Bi2O2Se has attracted much attention as a promising n-type eco-friendly thermoelectric material, especially for the n-type counterpart of p-type BiCuSeO. However, very poor electrical conductivity of intrinsic polycrystalline Bi2O2Se prohibits the further development of its thermoelectric performance. In the present work, a novel and facile method using a kitchen blender was developed for large-scale production of Bi2O2Se nanosheets. The electrical transport behavior of the resultant bulk Bi2O2Se via shear exfoliation changes from semiconductivity to metallic, electrical conductivity, which is greatly improved by more than 3 orders of magnitude from 0.1 to 470 S cm-1 at room temperature. Besides, thermal conductivity had been reduced to 0.93 W K-1 m-1 at 773 K. This synergistical promotion of electron-phonon transport could mainly come from increased interfacial defects of shear-exfoliated Bi2O2Se to introduce a large amount of electrons by Se vacancies and induce the intensive scattering of phonons by vacancies and interfaces. A high ZTpeak of 0.5 at 793 K had been achieved for Bi2O2Se with shear exfoliation for 60 min, which is 1.5 times larger than the ZT record of Bi2O2Se-based thermoelectrics. In addition, the figure of merit for the thermoelectric module based on p-type BiCuSeO and n-type Bi2O2Se has been evaluated to be around 0.8 at 793 K, making BiCuSeO-Bi2O2Se module a very promising candidate for mid-temperature thermoelectric applications.