BiSe with intrinsic low thermal conductivity has considered as a promising thermoelectric (TE) material at nearly room temperature. To improve its low thermoelectric figure of merit (zT), in this work, Sb and Te isovalent co-alloying was performed and significantly optimized its TE property with weakly anisotropic characteristic. After substituting Sb on Bi sites, the carrier concentration is suppressed by introduction of Sb- Se site defects, which contributes to the increased absolute value of Seebeck coefficient (|S|). Further co-alloying Te on Se of the optimized composition Bi_0.7Sb_0.3Se, the carrier concentration increased without affecting the |S| due to the enhanced effective mass, which leads to a highest power factor of 12.8 μW/(cm·K²) at 423 K. As a result, a maximum zT of ~0.54 is achieved for Bi_0.7Sb_0.3Se_0.7Te_0.3 along the pressing direction and the average zT (zT_ave) (from 300 K to 623 K) are drastically improved from 0.24 for pristine BiSe sample to 0.45. Moreover, an energy conversion efficiency ~4.0% is achieved for a single leg TE device of Bi_0.7Sb_0.3Se_0.7Te_0.3when applied the temperature difference of 339 K, indicating the potential TE application.

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.

Thermoelectric thin film has attracted a lot of attention due to its potential in fabricating micropower generator in chip sensors for internet of things (IoT). However, the undeveloped performance of n-type thermoelectric thin film limits its widely application. In this work, a facile post-selenization diffusion reaction method is employed to introduce Se into Bi₂Te₃ thin films, in order to optimize the carrier transport properties. Experimental and theoretical calculation results indicate that the carrier concentration decreases and density of states increases after Se doping, leading to the enhancement of Seebeck coefficient. Further, adjusting the diffusion reaction temperature can maintain the carrier concentration while increasing the mobility simultaneously, resulting in a high power factor of 1.5 mW/(m·K²), which is eight times higher than that of the pristine Bi₂Te₃ thin films. Subsequently, a thin film device fabricated by the present Se-doped Bi₂Te₃ thin films shows the highest output power of 60.20 nW under the temperature difference of 37 K, indicating its potential for practical use.

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)−yPb_xCuSeO (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.