Enhanced Thermoelectric Performance in n-Type Bi₂O₂Se by an Exquisite Grain Boundary Engineering Approach

Te-free n-type Bi2O2Se is one of the promising thermoelectric materials due to its high chemical stability and eco-friendliness. However, its conversion efficiency reported so far is still low. Hence, it is crucial to elevate its thermoelectric performance to realize eco-friendly widespread applications in heat recovery. In the present work, we introduce a facile method for exquisite grain boundary engineering with considerable chemical tunability. Herein, Bi is introduced in Bi2O2Se via a two-step heating route to construct a thermally induced atomically controlled grain boundary environment. Specifically, interface-related carrier/phonon transport greatly improves electrical conductivity without deteriorating the Seebeck coefficient, which leads to strong enhancement in the power factor. Meanwhile, intended grain boundaries and the induced Bi nanocomposition by tailoring the Bi content can strengthen the phonon scattering, which progressively suppresses the lattice thermal conductivity. Consequently, a high ZT of 0.47 at 773 K is obtained for the Bi2.03O2Se sample, which is over 50% improvement as compared to the pristine Bi2O2Se. These outcomes not only verify the efficacy of using the thermally induced atomically controlled grain boundary approach for interfacial modification but also open up a thermodynamic route to improve the performance of thermoelectric materials.