Understanding the Role of an Oxygen-Passivated Grain Boundary in Modulating the Thermoelectric Properties of a Sb2Te3 Thin Film

The present study demonstrates the effectiveness of incorporating O atoms into a Sb2Te3 thin film, leading to an improved power factor and a reduction in thermal conductivity. Based on the experimental evidence, it can be inferred that oxygen-related impurities preferentially wet the grain boundary (GB) and introduce a double Schottky barrier at the GB interface, promoting energy-dependent carrier scattering and ultimately leading to a rise in the Seebeck coefficient. Furthermore, the presence of O leads to the formation of highly dispersed and degenerate band pockets at the Fermi level of Sb2Te3, which results in a notable enhancement of the power factor while maintaining electrical mobility. These factors collectively contribute to an improved thermoelectric performance. A set of scanning probe microscopy techniques are used to experimentally confirm the alteration in charge transport resulting from the oxygen-passivated GB. Additionally, scanning thermal microscopy is employed to observe the spatial variations of thermal conductivity at the nanoscale regime. This study presents a comprehensive microscopic investigation of the impact of O on the phonon and charge-carrier-transport characteristics of Sb2Te3 thermoelectric materials and indicates that incorporating O may represent a feasible approach to improving the thermoelectric efficiency of these materials.