Raising the solubility of Gd yields superior thermoelectric performance in n-type PbSe

Abstract

Chemical doping is an indispensable means of improving the performance of thermoelectric materials, while one bottleneck for maximizing optimization is the low solubility of dopants. Here, we report a striking new insight that the more electronegative Br doping not only synergistically optimizes the carrier concentration and enhances the electron mobility, but also promotes the solubility limit of Gd in the n-type PbSe matrix, which is beneficial for Gd to flatten the conduction band. This is a successful strategy to improve the Seebeck coefficient to maximize the power factor. Concurrently, the anomalous strain field induced by atomic disorder and dislocation in the n-type Pb_1−yGd_yBr_0.003Se_0.997 system strongly scatters multi-frequency phonons, which reduces the lattice thermal conductivity markedly. As a result, a superior figure of merit (zT) value of ∼1.4 at 873 K and ultra-high power factor in a wide-temperature range are achieved for n-type Pb_0.997Gd_0.003Br_0.003Se_0.997. This work provides a unique paradigm to improve thermoelectrics by increasing the solid solubility of dopants.