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

Abstract

To improve thermoelectric performance of materials, the utilization of low-dimensional materials with a multi-alloy system is a promising approach. We report on the enhanced thermoelectric properties of n-type Bi 2 (Se x te 1−x) 3 nanoplates using solvothermal synthesis by tuning the composition of selenium (Se). Variation of the Se composition within nanoplates is demonstrated using X-ray diffraction and electron probe microanalysis. The calculated lattice parameters closely followed Vegard's law. However, when the Se composition was extremely high, an impurity phase was observed. At a reduced Se composition, regular-hexagonal-shaped nanoplates with a size of approximately 500 nm were produced. When the Se composition was increased, the shape distribution became random with sizes more than 5 μm. To measure the thermoelectric properties, nanoplate thin films (NPTs) were formed on a flexible substrate using drop-casting, followed by thermal annealing. The resulting NPTs sufficiently adhered to the substrate during the bending condition. The electrical conductivity of the NPTs increased with an increase in the Se composition, but it rapidly decreased at an extremely high Se composition because of the presence of the impurity phase. As a result, the Bi 2 (Se x te 1−x) 3 NPTs exhibited the highest power factor of 4.1 μW/(cm•K 2) at a Se composition of x = 0.75. Therefore, it was demonstrated that the thermoelectric performance of Bi 2 (Se x te 1−x) 3 nanoplates can be improved by tuning the Se composition. With the development of information technology including the Internet of things (IoT), the importance of thermoelectric materials that form flexible thin films has increased. This is because thermoelectric materials can directly convert thermal energy to electrical energy and vice versa. The electrical energy generated from the thermal energy via the Seebeck effect can be used to power wireless and wearable sensors 1-4. The thermal energy produced from electrical energy via the Peltier effect can be used to cool electronic devices 5-7. In both cases, the energy conversion efficiency depends on the dimensionless figure-of-merit ZT, defined as ZT = S 2 σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. In addition, the power factor PF defined by PF = S 2 σ is an important material property. Among thermoelectric materials, bismuth telluride-based alloys which were developed in the 1950s are the most suitable materials for application to IoT technology 8-10. This is because they exhibit the highest thermoelectric properties near 300 K. At this temperature, thermoelectric materials can be used as both thermoelectric generators and Peltier coolers. In particular, ternary alloys such as Bi 2 (Se x Te 1-x) 3 are known to exhibit superior performance compared to binary alloys such as Bi 2 Te 3 and Bi 2 Se 3 11-14. Bismuth telluride-based alloys including binary and ternary alloys commonly have rhombohedral tetradymite-type crystal str...

Energy‐Saving Pathways for Thermoelectric Nanomaterial Synthesis: Hydrothermal/Solvothermal, Microwave‐Assisted, Solution‐Based, and Powder Processing

“…An n ‐type Bi 2 (Se x Te 1− x ) 3 NPts with enhanced TE properties were prepared via ST synthesis (200 °C for 20 h) by adjusting the composition of Se. [ 185 ] Bi 2 O 3 , SeO 2 , TeO 2 , EG, PVP, and NaOH were used to prepare the precursor solution. At a Se composition of 0.08, regular‐hexagonal NPts (diameter ≈500 nm; thickness < 50 nm) were formed; when the Se composition was increased from 0.25 to 0.58, the edge length of the NPts increased and their shape gradually shifted away from the regular hexagon; when the Se composition was increased to 0.75, the plate size varied from 0.5 to 3 µm, and the plate shape became random.…”

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

“…Bending tests were performed when the two samples (the integrated nanocomposite film and nanoplate film with no SWCNTs) were attached to the surface of the bending plastic with a radius of 20 mm. The basic procedure is described in our previous report 57 . When the samples were repeatedly bent 500 times, the resistance was measured every tenth time.…”

Investigation of Phase Transition from Critical Nucleus to Bi2Te3 Nanoplate Based on Screw Dislocation‐Driven Spiral Growth by Solvothermal Synthesis

“…Therefore, we prepared the hexagonal nanoplates of Bi 2 Te 3 by solvothermal synthesis. [25][26][27][28][29][30] To obtain the low-dimensional effect in the 2D nanoplates, the size of the nanoplates should be small. However, the initial stage of the crystal growth of nanoplates has not been sufficiently investigated.…”