Outstanding Robust Photo- and Thermo-Electric Applications with Stabilized n-Doped Carbon Nanotubes by Parylene Coating

Abstract

Stabilization techniques for n-doped carbon nanotubes (CNTs) are essential for the practical use of CNT devices. However, none of the reported n-dopants have sufficient robustness in a practical environment. Herein, we report a highly stable technique for fabricating n-doped CNT films. We elucidate the mechanism by which air stability can be achieved by completely covering CNTs with n-dopants to prevent oxidation; consequently, the stability is lost when exposed to scratches or moisture. Therefore, we introduce parylene as a protective layer for n-doped CNTs and achieve air stability for more than 365 d. Moreover, we demonstrate outstanding robust thermo-electric power generation from strong acids, alkalis, and alcohols, which cannot be realized with conventional air-stable n-dopants. The proposed stabilization technique is versatile and can be applied to various n-dopants. Thus, it is expected to be a key technology in the practical application of CNT devices.

Synergistic Interactions in Sequential Process Doping of Polymer/Single‐Walled Carbon Nanotube Nanocomposites for Enhanced n‐Type Thermoelectric Performance

“…To ensure the achievement of a stable n‐type thermoelectric performance, it is crucial to avoid utilizing low doping concentrations of N‐DMBI, which are susceptible to secondary doping by oxygen in the surrounding environment. [ 59 ] As reported by Nakashima et al., the latter effect would result in a reversion to p‐type performance. [ 60 ] As demonstrated in the preceding sections, the NDI‐T1/SWCNT and NDI‐T2/SWCNT nanocomposites exhibit similar n‐type performances at high doping concentrations, while the undoped NDI‐T2/SWCNT exhibits a slightly higher p‐type performance.…”

Thermoelectric materials produced from single-wall carbon nanotubes

“…However, a considerable difference in thermal stability is observed between SWCNTs doped with small crown ether complexes and supramolecular dopants with an aromatic structure. The unprecedented air stability of the latter has led to the development of flexible TE generators that can function under practical conditions [41]; after parylene-C passivation, these SWCNTs have also been used under harsh environments [42].…”

n-Type PVP/SWCNT Composite Films with Improved Stability for Thermoelectric Power Generation

“…However, these electron-rich dopants are soluble in water although they can prevent the penetration of oxygen from air by coating on the CNTs, − resulting in degraded stability and performance due to chemical reaction with water. Suzuki et al deposited the protection layer of parylene on n-type CNTs by the chemical vapor deposition (CVD) method, which shows good stability in air for more than one year due to the hydrophobic property of parylene, whereas CVD has a high cost and a low rate, limiting large-scale applications. Thus, whether there are other methods to fabricate coating on the surface of SWCNTs and whether there are materials that not only adjust the conduction characteristic of SWCNTs but also do not react with both oxygen and water remain unknown.…”

“…These results suggest that coating technology is a feasible means to improve the stability of carbon tubes. However, these electron-rich dopants are soluble in water although they can prevent the penetration of oxygen from air by coating on the CNTs, − resulting in degraded stability and performance due to chemical reaction with water. Suzuki et al deposited the protection layer of parylene on n-type CNTs by the chemical vapor deposition (CVD) method, which shows good stability in air for more than one year due to the hydrophobic property of parylene, whereas CVD has a high cost and a low rate, limiting large-scale applications.…”