Boosting the thermoelectric performance of Bi 2 O 2 Se by isovalent doping

N ‐type Bi 2 O 2 Se has a bright prospect for mid‐temperature thermoelectric applications on account of the intrinsically low thermal conductivity. However, the low carrier concentration of Bi 2 O 2 Se (~10 15 cm −3 ) severely limits its thermoelectric performance. Herein, the boosting of the carrier concentration to ~10 19 cm −3 can be realized in our La‐doped Bi 2 O 2 Se 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 Bi 2 O 2 Se, and the point defects can also suppress the lattice thermal conductivity in La‐doped Bi 2 O 2 Se. The ZT value can be enhanced by a factor of ~4.5 to 0.35 at 823 K for Bi 1.98 La 0.02 O 2 Se as compared to the pristine Bi 2 O 2 Se. The coordinated optimization of electrical and thermal properties demonstrates an effective method for the rational design of high‐performance thermoelectric materials.