Heterostructured Bismuth Telluride Selenide Nanosheets for Enhanced Thermoelectric Performance

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Bismuth telluride (Bi2Te3) and bismuth selenide (Bi2Se3) are established n-type semiconductors for low-temperature thermoelectric applications.
• Achieving high thermoelectric efficiency requires optimizing material structure and properties to enhance the power factor and reduce thermal conductivity.

Purpose of the Study:

• To develop a facile synthesis method for core/shell heterostructured Bi2Te2Se/Bi2Te3 nanosheets.
• To investigate the structural characteristics and their influence on thermoelectric properties.
• To demonstrate the transformation of heterostructures into alloyed structures for improved thermoelectric performance.

Main Methods:

• Colloidal synthesis was employed to produce Bi2Te3, Bi2Se3, and heterostructured Bi2Te2Se/Bi2Te3 nanosheets.
• Spark plasma sintering was used to process the nanosheets into nanostructured bulks.
• Thermal annealing was utilized to controllably transform the core/shell structure into an alloyed structure.

Main Results:

• Core/shell heterostructured Bi2Te2Se/Bi2Te3 nanosheets (1-3 μm lateral dimensions, ~50 nm thickness) with nanosized pores were successfully synthesized.
• The heterostructures exhibited inhomogeneous chalcogen distribution, forming selenium and tellurium-rich layers, promoting phonon scattering.
• Annealed alloyed pellets (Bi2Te2.55Se0.45) showed low thermal conductivity and a high in-plane power factor, achieving a thermoelectric figure of merit (zT) of 1.34 at 400 K.

Conclusions:

• The core/shell heterostructure design effectively enhances phonon scattering, contributing to improved thermoelectric properties.
• Controllable transformation from heterostructured to alloyed structures offers a pathway to optimize thermoelectric materials.
• The synthesized Bi2Te2.55Se0.45 material demonstrates significant potential for efficient low-temperature thermoelectric energy conversion.