Enabling Oxidation Protection and Carrier-Type Switching for Bismuth Telluride Nanoribbons via in Situ Organic...

Thermoelectric materials with high electrical conductivity and low thermal conductivity (e.g., Bi₂Te₃) can efficiently convert waste heat into electricity; however, in spite of favorable theoretical predictions, individual Bi₂Te₃ nanostructures tend to perform less efficiently than bulk Bi₂Te₃. We report a greater-than-order-of-magnitude enhancement in the thermoelectric properties of suspended Bi₂Te₃ nanoribbons, coated in situ to form a Bi₂Te₃/F₄-TCNQ core-shell nanoribbon without oxidizing the core-shell interface. The shell serves as an oxidation barrier but also directly functions as a strong electron acceptor and p-type carrier donor, switching the majority carriers from a dominant n-type carrier concentration (∼10²¹ cm^-3) to a dominant p-type carrier concentration (∼10²⁰ cm^-3). Compared to uncoated Bi₂Te₃ nanoribbons, our Bi₂Te₃/F₄-TCNQ core-shell nanoribbon demonstrates an effective chemical potential dramatically shifted toward the valence band (by 300-640 meV), robustly increased Seebeck coefficient (∼6× at 250 K), and improved thermoelectric performance (10-20× at 250 K).