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Precisely Tailored Thermoelectric Properties of Carbon Nanotubes(CNTs) via Selective Inkjet Printing

  • Woojin Kim (김우진, KU-KIST융합대학원 NBIT융합전공)

초록/요약

With increasing demands for self-powered wearable electronics, flexible thermoelec-tric (TE) devices harvesting electrical energy from body heat have drawn significant at-tention. Numerous promising material candidates have been explored for realizing highly reliable flexible TE devices. Among them, carbon nanotubes (CNTs) offer notable TE properties, mechanical flexibility, and solution processability which provide attractive advantages to meet these requirements. However, there have been critical bottlenecks of low electrical conductivity of CNTs, resulting in the poor Figure-of-Merit (zT). To ad-dress these challenges, extensive research has focused on enhancing the electrical con-ductivity and Seebeck coefficient of pristine CNTs through surface charge transfer dop-ing. However, most conventional doping methods, such as solution dipping or vaporized deposition, are applied across the entire CNT film surface, therefore, it difficult to pre-cisely control the thermoelectric performance. In this study, we report a doping strategy via inkjet printing to tailor the TE proper-ties of CNT films using poly(acrylic acid) (PAA) as a p-type dopant. By optimizing the concentration of the PAA inks, we achieved enhanced TE performance in CNT films. The concentration-dependent control of doping levels enabled an optimal balance be-tween electrical conductivity and the Seebeck coefficient, resulting in maximum TE per-formance at a specific concentration (30 mg mL-1). To investigate the effect of localized selective doping on the TE properties of CNT films, full-area and half-area doping were conducted at the optimized PAA concentration. Notably, the half-doped CNT film exhibited a higher Seebeck coefficient (50.479 μV/K) than full-are doped films, despite showing a lower electrical conductivity. This indicates that concentration and mobility gradients across the film contribute to the enhancement of Seebeck voltage. The observed properties in the half-doped film indicate that the spa-tial gradient played a dominant role in determining TE properties. The selective doping-induced inhomogeneity created an internal potential gradient amplifying the thermoelec-tric response. In the half-doping condition, the spatial gradients of carrier concentration and mobility were favorably tuned, resulting in an enhanced Seebeck response. Therefore, our study demonstrates that the inkjet printing-based doping method for CNTs not only enables precise control of doping levels over TE properties but also offers a scalable and versatile approach for designing high-performance TE materials.

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목차

1. INTRODUCTION 1
1.1. Fundamental of thermoelectrics 1
1.2. Inkjet printing 7
2. Research progress in thermoelectric materials 10
2.1. Inorganic thermoelectric materials 13
2.2. Organic thermoelectric materials 17
2.3. CNT thermoelectric 21
3. Motivation 26
4. Experimental Section 29
4.1. Procedure of CNT dispersion and film fabrication 29
4.2. Preparation of Poly(acrylic acid) ink and doping method 29
4.3. Characterization of the pristine and doped CNT film 30
5. Results and Discussion 31
6. CONCLUSION 44
REFERENCES 45

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