Remarkably Stable, High‐Quality Semiconducting Single‐Walled Carbon Nanotube Inks for Highly Reproducible Field‐Effect Transistors

Abstract

production of low-cost network field-effect transistors (FETs), [1] logic circuits, [2,3] and other electronic devices. [4][5][6][7][8] The polymerwrapping selection of semiconducting SWCNT was introduced by Nish et al. in 2007, [9] and improved and expanded by many authors in the last years. [10][11][12][13][14][15][16][17][18][19][20] Polyfluorene, [18,21,22] poly thiophene [23][24][25][26] derivatives, and many other polymers [27][28][29][30][31][32] are used to interact with the SWCNT walls. [33][34][35][36] However, the interaction of the polymer chains with the SWCNT is rather weak, resulting in the main advantage of this sorting method, namely the polymer wrapping does not greatly alter the electronic properties of the nanotubes. [37][38][39] In the last years, this technique has become very popular as compared with other solution-based selection processes such as density gradient ultracentrifugation and gel chromatography, in particular because of its simplicity, scalability, and high dispersion yield. [36,40,41] The mechanism of the selection process of s-SWCNT, even if still under debate, can be described as following. First, the π-π interaction is driving the polymer backbone to the SWCNT walls, and the alkyl side chains wrap around the tube limiting its interaction with the solvent. Second, the selection mechanism, as it has been speculated, arises from the screening of the s-SWCNT polarizability by wrapped poly mers. [12] The metallic-SWCNT (m-SWCNT) species have roughly three orders of magnitude larger polarizability as compared with the s-SWCNT. [42,43] It is, therefore, the large polarizability and the insufficient screening that lead to the rebundling of the m-SWCNT. [23] The significant weight difference between bundles and individualized tubes is the last ingredient, which allows for the separation of the two species by means of ultracentrifugation.Not only the polymer structure but also the chain conformation in the solvent is an important factor to obtain high selectivity and high dispersion yield. Wang et al. investigated different organic solvents for the selection process bringing forward the idea that a poor solvent for the polymer is necessary to reduce the polymer-solvent interaction and favor the interaction with the SWCNT walls. [20] Toluene has been the most used solvent as it allows to obtain a good selection yield for semiconducting tubes with many different polymers. [11,13,18,24,44,45] Unfortunately, though, the shelf lifetime of s-SWCNT inks in toluene is severely limited by nanotube aggregation and In the past years, high-quality semiconducting single-walled carbon nanotube (s-SWCNT) inks obtained by conjugated polymer wrapping using toluene as solvent have been used for the fabrication of high-performance field-effect transistors. Charge-carrier mobilities up to 50 cm 2 V −1 s −1 and on/off ratios above 10 8 have been reported for devices based on networks of s-SWCNT. However, devices fabricated from inks that are only a few weeks old generally show a marked decrease in perf...

Phenanthroline Additives for Enhanced Semiconducting Carbon Nanotube Dispersion Stability and Transistor Performance

“…As demonstrated previously by Talsma et al , UV–vis–NIR absorption spectroscopy is a very simple but effective tool to monitor time-dependent aggregation and thus ink aging via decreasing optical density. This effect is shown in Figure a for a dispersion of (6,5) SWCNTs in toluene with a minimum of residual PFO-BPy and a nanotube concentration sufficiently high to observe aggregation on a reasonable timescale while maintaining linearity of the detector.…”

Synaptic Plasticity in Semiconducting Single‐Walled Carbon Nanotubes Transistors

“…Preparation and Characterization of Semiconducting SWCNT Dispersion: HiPCO SWCNT inks were prepared and characterized as described in our previous work. [43] Field-Effect Transistor Fabrication and Electrical Characterization: FETs were fabricated on silicon substrates with a thermally grown SiO 2 layer of about 230 nm in thickness. Source and drain bottom electrodes (10 nm ITO/30 nm Au) were lithographically defined.…”

Customizing the Polarity of Single‐Walled Carbon‐Nanotube Field‐Effect Transistors Using Solution‐Based Additives

“…For this purpose, the supernatant obtained after the first ultracentrifugation is centrifuged for 5 h at 55 000 rpm (367 000 g ), where the individualized s‐SWNTs precipitates to form a pellet, and the free polymer remains in the supernatant. Finally, the pellet is re‐dispersed by sonication in the solvent of choice in this case o‐xylene 48…”