Impact of the amount of single-wall carbon nanotubes (SWCNTs) in single-crystalline Bi₂Te₃ nanoplates/SWCNTs nanocomposite films by drop-casting method

Abstract

To investigate the effect of adding single-wall carbon nanotubes (SWCNTs) to Bi 2 Te 3 nanoplate thin films, we prepared Bi 2 Te 3 nanoplate/SWCNTs nanocomposite thin films with different amounts of SWCNTs using a drop-casting technique. The Bi 2 Te 3 nanoplates prepared by solvothermal synthesis exhibited a single-crystalline phase with rhombohedral crystal structure. The nanoplates had flat surfaces with edge size of approximately 1 μm. The completed nanocomposite thin films were thermally annealed at 250 °C to improve their electrical conductivity. The electrical conductivity of the nanocomposite thin films with added SWCNTs improved, but the power factor decreased compared to those of the Bi 2 Te 3 nanoplate thin film. This occurred because the quality of Bi 2 Te 3 nanoplates in the nanocomposite thin films decreased due to excessive annealing as the introduced SWCNTs have high thermal conductivity. Therefore, we reduced the annealing temperature of nanocomposite thin films to 225 °C and found that the power factor was significantly improved.

Flexible thermoelectric films formed using integrated nanocomposites with single-wall carbon nanotubes and Bi2Te3 nanoplates via solvothermal synthesis

“…This is a remarkable phenomenon considering that the added SWCNTs possess a positive Seebeck coefficient. In our previous study, in which SWCNTs were added to the films during drop-casting, but excluding solvothermal synthesis, the Seebeck coefficient became less negative as the SWCNT-ethanol solution increased 37 . The mechanism of this phenomenon is not clear, but one possible explanation is that the contact resistance between the Bi 2 Te 3 nanoplates and SWCNTs decreased owing to the integration of the materials.…”

“…In Table 1, we compare the thermoelectric properties of the integrated nanocomposite film with the maximum power factor in this study (SWCNT-ethanol solution of 9 mL) to those of the reference sample, which was a simple nanocomposite film formed in our previous study by adding SWCNTs during drop-casting, but excluding solvothermal synthesis 37 . A reference sample containing the same carbon mass concentration was chosen for comparison.…”

“…In our previous study, to reduce the size and dimension of bismuth telluride-based alloys, single-crystalline Bi 2 Te 3 nanoplates (quasi-2D material) with a thickness of several tens of nanometers were synthesized using a solvothermal method 34,35 . After the nanoplate fabrication, flexible thin films were prepared by mixing the Bi 2 Te 3 nanoplates and SWCNTs by drop-casting 36,37 . Although the Bi 2 Te 3 nanoplates and SWCNTs had high electrical conductivities individually, the conductivity decreased after mixing, owing to the high contact resistance between them.…”

Solvothermal synthesis of n-type Bi2(SexTe1−x)3 nanoplates for high-performance thermoelectric thin films on flexible substrates

“…To measure the thermoelectric properties of the Bi 2 (Se x Te 1−x ) 3 nanoplates, NPTs were prepared via drop-casting 35,36 . The outline of the drop-casting process is described in the supplemental information provided in Fig.…”

Effects of Preparation Methods on the Thermoelectric Performance of SWCNT/Bi2Te3 Bulk Composites

“…Carbon nanotubes (CNTs) have extraordinary electrical and mechanical properties [13,14] and can form conductive network structures in a relatively low threshold value when used as fillers for preparation of composite materials; therefore, introducing CNTs into inorganic TE matrixes is an effective method to further improve the TE properties of inorganic materials [15][16][17][18][19][20]. For instance, Choi et al [15] prepared Te nanowires using a chemical method and then synthesized flexible single-walled carbon nanotube (SWCNT)/Te nanowire films via a vacuum filtering method, and a power factor of 3.40 µWm −1 K −2 was obtained for the composite film with 2 wt % SWCNTs at RT.…”