Realizing high thermoelectric performance via selective resonant doping in oxyselenide BiCuSeO

Tuning the charge carrier concentration is imperative to optimize the thermoelectric (TE) performance of a material. For BiCuSeO based oxyselenides, doping efforts have been limited to optimizing the carrier concentration. In the present work, dual-doping of In and Pb at Bi site is introduced for p-type BiCuSeO to realize the electric transport channels with intricate band characteristics to improve the power factor (PF). Herein, the impurity resonant state is realized via doping of resonant dopant In over Pb, where Pb comes forward to optimize the Fermi energy in the dual-doped BiCuSeO system to divulge the significance of complex electronic structure. The manifold roles of dual-doping are used to adjust the elevation of the PF due to the significant enhancement in electrical properties. Thus, the combined experimental and theoretical study shows that the In/Pb dual doping at Bi sites gently reduces bandgap, introduces resonant doping states with shifting down the Fermi level into valence band (VB) with a larger density of state, and thus causes to increase the carrier concentration and effective mass (m*), which are favorable to enhance the electronic transport significantly. As a result, both improved ZT(max) = 0.87 (at 873 K) and high ZT(ave) = 0.5 (at 300-873 K) are realized for InyBi((1-x)-y)Pb(x)CuSeO (where x = 0.06 and y = 0.04) system. The obtained results successfully demonstrate the effectiveness of the selective dual doping with resonant dopant inducing band manipulation and carrier engineering that can unlock new prospects to develop high TE materials.