Boosting the thermoelectric performance of Bi₂O₂Se by isovalent doping

N-type Bi₂O₂Se has a bright prospect for mid-temperature thermoelectric applications on account of the intrinsically low thermal conductivity. However, the low carrier concentration of Bi₂O₂Se (~10¹⁵ cm⁻³) severely limits its thermoelectric performance. Herein, the boosting of the carrier concentration to ~10¹⁹ cm⁻³ can be realized in our La-doped Bi₂O₂Se ceramic samples, which could be ascribed to the formation of isoelectronic traps and the narrowing of band gap, and contribute to a marked increase in the electrical conductivity (from 0.03 S cm⁻¹ to 182 S cm⁻¹). Our X-ray absorption near-edge structure spectra results reveal that a local disordering of oxygen atoms could be an important reason for the intrinsically low thermal conductivity of Bi₂O₂Se, and the point defects can also suppress the lattice thermal conductivity in La-doped Bi₂O₂Se. The ZT value can be enhanced by a factor of ~4.5 to 0.35 at 823 K for Bi_1.98La_0.02O₂Se as compared to the pristine Bi₂O₂Se. The coordinated optimization of electrical and thermal properties demonstrates an effective method for the rational design of high-performance thermoelectric materials.