Bi(Te, Se)-based compounds have attracted lots of attention for nearly two centuries as one of the most successful commercial thermoelectric (TE) materials due to their high performance at near room temperature. Compared with 3D bulks, 2D thin films are more compatible with modern semiconductor technology and have unique advantages in the construction of micro- and nano-devices. For device applications, high average TE performance over the entire operating temperature range is critical. Herein, highly c-axis-oriented N-type Bi(Te, Se) epitaxial thin films have been successfully prepared using the pulsed laser deposition technology by adjusting the deposition temperature. The film deposited at ~260 ℃ demonstrate a remarkable average power factor (PF_ave) of ~24.4 μW·cm⁻¹·K⁻² over the temperature range of 305–470 K, higher than most of the state-of-the-art Bi(Te, Se)-based films. Moreover, the estimated average zT value of the film is as high as ~0.81. We then constructed thin-film TE devices by using the above oriented Bi(Te, Se) films, and the maximum output power density of the device can reach up to ~30.1 W/m² under the temperature difference of 40 K. Predictably, the outstanding average TE performance of the highly oriented Bi(Te, Se) thin films will have an excellent panorama of applications in semiconductor cooling and power generation.

AgBi₃S₅ is a new n-type thermoelectric material that is environmentally friendly and composed of elements of earth-abundant, non-toxic and high performance-cost ratio. This compound features an intrinsically low thermal conductivity derived from its complex monoclinic structure. However, the terrible electrical transport properties greatly limited the improvement of thermoelectric performance. Most previous studies considered that carrier concentration is the main reason for low electrical conductivity and focused on improving carrier concentration by aliovalent ion doping. In this work, we found that the critical parameter that restricts the electric transport performance of AgBi₃S₅ was the extremely low carrier mobility instead of the carrier concentration. According to the Pisarenko relationships and density functional theory calculations, Nb doping can sharpen the conduction band of AgBi₃S₅, which contributes to reducing the effective mass and improving the carrier mobility. With a further increase of the Nb doping content, the conduction band convergence can enlarge the effective mass and preserve the carrier mobility. Combined with the decrease in lattice thermal conductivity due to the intensive phone scattering, a maximum ZT value of ~0.50 at 773 K was achieved in Ag_0.97Nb_0.03Bi₃S₅, which was ~109.6% higher than that of pure AgBi₃S₅. This work will stimulate the new exploration of high-performance thermoelectric materials in ternary metal sulfides.