After more than three decades of molecular and carbon-based electronics, the creation of airand thermally stable n-type materials remains a challenge in the development of future p/n junction devices such as solar cells and thermoelectric modules. Here we report a series of ordinary salts such as sodium chloride (NaCl), sodium hydroxide (NaOH) and potassium hydroxide (KOH) with crown ethers as new doping reagents for converting single-walled carbon nanotubes to stable n-type materials. Thermoelectric analyses revealed that these new n-type single-walled carbon nanotubes displayed remarkable air stability even at 100 o C for more than one month. Their thermoelectric properties with a dimensionless figure-of-merit (ZT) of 0.1 make these new n-type single-walled carbon nanotubes a most promising candidate for future n-type carbon-based thermoelectric materials.
The thermally-triggered n-type doping of single-walled carbon nanotubes is demonstrated using 1,1'-bis(diphenylphosphino)ferrocene, a novel n-type dopant. Through a simple thermal vacuum process, the phosphine compounds are moderately encapsulated inside single-walled carbon nanotubes. The encapsulation into SWNTs is carefully characterized using Raman/X-ray spectroscopy and transmission electron microscopy. This easy-to-handle doping with air-stable precursors for n-type SWNTs enables the large-scale fabrication of thermoelectric materials showing an excellent power factor exceeding approximately 240 μW mK(-2) .
This study investigates the hydride-mediated electron transfer doping of single-walled carbon nanotubes using absorption spectroscopy and thermoelectric measurements. Specific solvent basicity is found to be important for the efficient n-type doping of carbon nanotubes. This progress is an essential requirement for the future development of electronic and energy devices.
Aqueous surfactant dispersion is the most typical starting step to functionalize materials consisting of carbon nanotubes, but the effects of surfactants on the electronic properties are stillu nclear.H ere we report how the functional groups of surfactants affect the electronic properties of carbon nanotube films. Using spectroscopic and thermoelectric characterization, we demonstrate that anionic and non-ionic surfactants contribute to the formation of p-type and n-type carbonn anotubes, respectively.A dditionally,p -type doping with oxygen adsorptioni sf ound to competew ith surfactants' doping. These findings are useful for designing the srarting carbon nanotube materials exhibitingd esirable electronic properties. Results and DiscussionHerein we show the effect of the functional groups in surfactants including sulfonate,c arboxylate, and nonionic polyethy- [a] Prof.
The self-assembly of Prussian blue nanoparticles and singlewalled carbon nanotubes is demonstrated by using analytical TEM. The nanotube composites containing compositionally tunable Prussian blue nanoparticles are, for the first time, applied to finely modulate their Seebeck coefficients.Prussian blue (PB) is an ancient, but novel functional inorganic pigment with porous coordination polymer structures. Thermoelectric materials based on single-walled carbon nanotubes (SWNTs) are the most striking candidates for future flexible power generators. 13 Their degree of energy conversion is usually expressed as a dimensionless figure of merit, ZT = ¡ 2 ·T/¬, where ¡ is the Seebeck coefficient, · is electrical conductivity, T is temperature, and ¬ is thermal conductivity. SWNTs possess high electrical conductivity and structural flexibility but have the disadvantages of a small Seebeck coefficient and high thermal conductivity. To improve their figure of merit, polymer-composites were proposed as promising materials. In most cases, conducting polymers serve as efficient electrical conductors, and insulating polymers are useful for low thermal conductivity, which thus enhance ZT.13,14 On the other hand, a rational approach for improving the Seebeck coefficient of SWNTs is still a challenging subject. Because of the trade-off relationship between conductivity and the Seebeck coefficient, the Seebeck coefficient was usually sacrificed for increased electrical conductivity.13 Recently, we have successfully improved the Seebeck coefficient and ZT of SWNT composites by means of systematic molecular doping, in which the electrochemical redox potential of the dopant is a crucial parameter for efficient carrier generation. 15 We herein report the spontaneous formation of composites between SWNTs and compositionally tunable PB-NPs in which the Seebeck coefficient is systematically controlled with the composition of the PB-NPs.PB and three types of modified PB were used and are denoted as Fe [Fe(CN) 16 and the mixture was then filtered using a Teflon membrane. After vacuum drying at 80°C, a self-standing composite sheet was peeled from the membrane filter, as shown in Figure 1.First, we assessed the adsorptive nature of soluble PB-NPs onto SWNTs. Composites of PB-NPs and SWNTs (9:1 in weight) were dissolved in 1-butanol and drop-cast onto a carbon grid for transmission electron microscopy (TEM) observation. The all cubic PB-NPs were observed only on the surface of the SWNT fibers (Figures 2a2d), suggesting an intense adsorptive nature of the BP-NPs onto the SWNT fibers regardless of their elemental composition. No nanoparticles were present between Figure 1. Schematic illustration of fabrication of PB-NPs/ SWNT composites.
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