Carrier Type Switching in Bismuth Telluride through In-Situ Organic Molecule Coating

Thermoelectric materials have gained significant attention for their ability to efficiently convert waste heat into electricity. Among these materials, Bi₂Te₃ stands out as a near-room temperature thermoelectric material due to its exceptional properties, such as high electrical conductivity and relatively low thermal conductivity. Furthermore, low-dimensional Bi₂Te₃ nanostructures has also shown promise in enhancing thermoelectric properties, but it faces challenges, such as chalcogen vacancies and surface oxidation. To address these challenges, various methods have been proposed, including oxygen plasma treatment, superacid treatment, and atomic layer deposition (ALD) of Al₂O₃ to prevent surface oxidation. Simultaneously, several approaches have been explored to enhance thermoelectric properties of nanostructures through employing external dopant layer, such as tetrafluoro-tetracyanoquinodimethane (F₄-TCNQ). Here, we demonstrated the successful synthesis of Bi₂Te₃/F₄-TCNQ layered nanostructures through catalyst-free chemical vapor deposition (CVD). Even after a month of exposure to air, TEM analysis revealed an oxidation-free interface, confirming the efficacy of the coating as an oxygen diffusion barrier. In addition to this, the majority carrier type of the nanostructures switched from <i>n</i>-type to <i>p</i>-type and their Seebeck coefficient increased over an order-magnitude. It confirms that this in-situ organic layer coating not only provides an oxidation-protecting layer, but also act as a hole-injecting layer that can lead to a significant improve of thermoelectric characteristics. Finally, the F₄-TCNQ-coated Bi₂Te₃ exhibited an order-of-magnitude higher thermoelectric figure of merit (<i>zT</i>) that peaks at a minimum of 10–20 times improvement 250 K.