Enhancing Thermoelectric Efficiency of Bi₂Te₃ Nanoribbons Through In Situ F₄-TCNQ and Ex-Situ Cr Interfacial Alloying

Nanostructured Bi₂Te₃ has shown promise in enhancing thermoelectric characteristics as predicted theoretically. However, its practical performance often falls short of that of bulk Bi₂Te₃ due to defects, impurities, and surface oxidation. To address these issues, various techniques such as oxygen plasma treatment, non-oxidizing superacid treatment, and atomic layer deposition (ALD) of Al₂O₃, have been explored to precisely control the surface chemical potential of nanostructures, aiming for long-lasting and high-performance thermoelectric applications. Among these techniques, extrinsic doping by coating carrier-rich or metallic layers has shown potential in modulating carrier concentration and chemical potential.<br/>In this presentation, we introduce two distinct strategies to enhance the thermoelectric performance of Bi₂Te₃ nanoribbons through the incorporation of external dopant layers: an <i>in-situ</i> F₄-TCNQ layer and an <i>ex-situ</i> Cr layer. The in-situ coated F₄-TCNQ layer induces a transformation of the major carrier from <i>n</i>-type to <i>p</i>-type, resulting in sixfold enhancement of the Seebeck coefficient. At the same time, the core-shell structure effectively shields the Bi₂Te₃ core from oxidation, demonstrating no surface oxidation or loss of thermoelectric properties even after one month in ambient air.¹ On the other hand, the surface-coated Cr layer induces a 70% reduction in nanoribbon resistance along with a 24% increase in the Seebeck coefficient, resulting in twofold enhancement of thermoelectric figure of merit (<i>zT</i>). Moreover, we will share physical investigations of these enhanced thermoelectric characteristics through energy band simulation and Raman spectroscopy analysis. We expect our findings to provide an approach for nanostructured thermoelectric materials to achieve performance competitive with bulk materials while leveraging the inherent advantages of nanostructures.<br/><br/>1 Park, J. B.<i> et al.</i> Enabling Oxidation Protection and Carrier-Type Switching for Bismuth Telluride Nanoribbons via in Situ Organic Molecule Coating. <i>Nano Letters</i> <b>23</b>, 11395–11401 (2023).