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

Abstract

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 ZT peak 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.

Valance Band Maximum and Thermoelectric Properties of Bi\(_2\)O\(_2\)Se: First-Principles Calculations

“…Many methods have been used to improve the ZT of Bi 2 O 2 Se including: making point defects [6,11], introducing strains [14], nanostructure, etc. [15]. These methods do not improve the value of ZT to any considerable extent [15,16].…”

“…[15]. These methods do not improve the value of ZT to any considerable extent [15,16]. The highest values of ZT for bulk materials are usually around unity or a little higher [13,[17][18][19].…”

Optimization of electrical and thermal transport properties of layered Bi2O2Se via Nb doping

“…Aliovalent doping and vacancy engineering are effectives route to optimize the carrier concentration. For example, Ge and Sn replacing Bi [23,24], Cl substitution Se as well as Se vacancies have been performed [25,26]. Furthermore, replacing O with electropositive S or Te can significantly reduce the band gap and enhance the electrical conductivity as well [27,28].…”

An Update Review on N-Type Layered Oxyselenide Thermoelectric Materials

“…Different from BiCuSeO, the intrinsic Bi 2 O 2 Se exhibits n -type transport properties due to a large number of Se vacancies in the crystal structure [ 43 , 44 ]. However, the crystal structure of Bi 2 O 2 Se is very similar to BiCuSeO in which insulative [Bi 2 O 2 ] 2+ layers and conductive [Se] 2− layers stack along the c -axis alternatively [ 26 , 45 , 46 ].…”