Enhanced Near-Room-Temperature Thermoelectric Performance of Mg3Bi2 Through Ag Doping

Abstract

Mg₃Bi₂-based films are promising near-room-temperature thermoelectric materials for the development of flexible thermoelectric devices. However, the high hole concentration caused by the abundance of intrinsic Mg vacancies easily leads to deterioration of electrical properties, especially for p-type Mg₃Bi₂ film. And the optimization of thermal conductivity of the Mg₃Bi₂-based films is barely investigated. In this work, we demonstrate the improved thermoelectric performances of p-type Mg₃Bi₂ through Ag doping by magnetron sputtering. This doping successfully reduces the hole concentration and broadens the band gap of Mg₃Bi₂, thus resulting in a peak power factor of 442 μW m⁻¹ K⁻² at 525 K. At the same time, Ag doping-induced fluctuations in mass and microscopic strain effectively enhanced the phonon scattering to reduce the lattice thermal conductivity. Consequently, a maximum thermoelectric figure of merit of 0.22 is achieved at 525 K. Its near-room-temperature thermoelectric performances demonstrate superior performance compared to many Mg₃Bi₂-based films. To further evaluate its potential for thermoelectric power generation, we fabricated a thermoelectric device using Ag-doped Mg₃Bi₂ films, which achieved a power density of 864 μW cm⁻² at 35 K temperature difference. This study presents an effective strategy for the advancement of Mg₃Bi₂-based films for application in micro-thermoelectric devices.