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

Thermoelectric materials with high electrical conductivity and low thermal conductivity (e.g., Bi 2 Te 3 ) can efficiently convert waste heat into electricity; however, in spite of favorable theoretical predictions, individual Bi 2 Te 3 nanostructures tend to perform less efficiently than bulk Bi 2 Te 3 . We report a greater-than-order-of-magnitude enhancement in the thermoelectric properties of suspended Bi 2 Te 3 nanoribbons, coated in situ to form a Bi 2 Te 3 /F 4 -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 (∼10 21 cm -3 ) to a dominant p-type carrier concentration (∼10 20 cm -3 ). Compared to uncoated Bi 2 Te 3 nanoribbons, our Bi 2 Te 3 /F 4 -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).