Enhanced thermoelectric properties of n-type Bi₂O₂Se by KCl doping

Bi₂O₂Se is considered one of the most promising thermoelectric (TE) materials for combining with p-type BiCuSeO in a TE module given its unique chemical and thermal stability. However, the enhancement of its dimensionless figure of merit, zT value, remains a challenge because of its low electrical conductivity. Herein, we introduce KCl into Bi₂O₂Se, synthesized by solid-state reaction and spark plasma sintering method, to improve its TE properties. The synthesized samples show an outstanding enhancement in electrical conductivity, carrier concentration, and power factor after KCl doping. The Bi₂O₂Se-based sample with a 0.05% KCl doping content possesses a high zT value of ~0.58 at 773 K, which is over 50% enhancement compared with the pristine Bi₂O₂Se sample. We also prove that the K element substitutes the Bi site, and Cl replaces the Se site by X-ray diffraction results and density functional theory calculation, supporting that K can improve the electrical conductivity by the position of Fermi level which is above the conduction band minimum. Experimental and theoretical results indicate the success of co-doping with a small amount of KCl and show a huge potential of this novel method for Bi₂O₂Se TE performance improvement.