Enhanced thermal stability of Bi2Te3-based alloys via interface engineering with atomic layer deposition

Unlocking the Potential of Porous Bi2Te3-Based Thermoelectrics Using Precise Interface Engineering through Atomic Layer Deposition

Porous thermoelectric materials offer exciting prospects for improving the thermoelectric performance by significantly reducing the thermal conductivity. Nevertheless, porous structures are affected by issues, including restricted enhancements in performance attributed to decreased electronic conductivity and degraded mechanical strength. This study introduces an innovative strategy for overcoming these challenges using porous Bi0.4Sb1.6Te3 (BST) by combining porous structuring and interface engineering via atomic layer deposition (ALD). Porous BST powder was produced by selectively dissolving KCl in a milled mixture of BST and KCl; the interfaces were engineered by coating ZnO films through ALD. This novel architecture remarkably reduced the thermal conductivity owing to the presence of several nanopores and ZnO/BST heterointerfaces, promoting efficient phonon scattering. Additionally, the ZnO coating mitigated the high resistivity associated with the porous structure, resulting in an improved power factor. Consequently, the ZnO-coated porous BST demonstrated a remarkable enhancement in thermoelectric efficiency, with a maximum zT of approximately 1.53 in the temperature range of 333-353 K, and a zT of 1.44 at 298 K. Furthermore, this approach plays a significant role in enhancing the mechanical strength, effectively mitigating a critical limitation of porous structures. These findings open new avenues for the development of advanced porous thermoelectric materials and highlight their potential for precise interface engineering through the ALD.

Enhanced Contact Performance and Thermal Tolerance of Ni/Bi2Te3 Joints for Bi2Te3-Based Thermoelectric Devices

Ni metal has been widely used as a barrier layer in Bi₂Te₃-based thermoelectric devices, which establishes stable joints to link Bi₂Te₃-based legs and electrodes. However, the Ni/Bi₂Te₃ joints become very fragile when the devices were exposed to high temperature, causing severe performance deterioration and even device failure. Herein, stable Ni/Bi₂Te₃ joints have been established by arc spraying of the Ni barrier layer on the Bi₂Te₃-based alloys. The interface microstructure and contact performance including the bonding strength and contact resistivity of the arc-sprayed Ni/Bi₂Te₃ joints are investigated. The results indicate that, as compared with traditional Ni/Bi₂Te₃ joints, the arc-sprayed Ni/Bi₂Te₃ joints have comparably low contact resistivity while possessing a 50% higher bonding strength. Aging the joints as an exposure to high-temperature circumstances, the arc-sprayed Ni/Bi₂Te₃ joints exhibit much better tolerance to the thermal shock with stable bonding strength and contact resistivity. The enhanced interfacial contact performance and thermal tolerance should be attributed to the thick Ni barrier layer and interface reaction layer with good Ohmic contact. This work provides an effective strategy to establish stable joints for the Bi₂Te₃-based thermoelectric devices with improved thermal stability.

Carrier Modulation in Bi2Te3-Based Alloys via Interfacial Doping with Atomic Layer Deposition

The carrier concentration in Bi2Te3-based alloys is a decisive factor in determining their thermoelectric performance. Herein, we propose a novel approach to modulate the carrier concentration via the encapsulation of the alloy precursor powders. Atomic layer deposition (ALD) of ZnO and SnO2 was performed over the Bi2Te2.7Se0.3 powders. After spark plasma sintering at 500 °C for 20 min, the carrier concentration in the ZnO-coated samples decreased, while the carrier concentration in the SnO2-coated samples increased. This trend was more pronounced as the number of ALD cycles increased. This was attributed to the intermixing of the metal ions at the interface. Zn2+ substituted for Bi3+ at the interface acted as an acceptor, while Sn4+ substituted for Bi3+ acted as a donor. This indicates that the carrier concentration can be adjusted depending on the materials deposited with ALD. The use of fine powders changes the carrier concentration more strongly, because the quantity of material deposited increases with the effective surface area. Therefore, the proposed approach would provide opportunities to precisely optimize the carrier concentration for high thermoelectric performance.