RESUMO
Ultrapure semiconducting single-walled carbon nanotube (sc-SWNT) dispersions produced through conjugated polymer sorting are ideal candidates for the fabrication of solution-processed organic electronic devices on a commercial scale. Protocols for sorting and dispersing ultrapure sc-SWNTs with conjugated polymers for thin-film transistor (TFT) applications have been well refined. Conventional wisdom dictates that removal of excess unbound polymer through filtration or centrifugation is necessary to produce high-performance TFTs. However, this is time-consuming, wasteful, and resource-intensive. In this report, we challenge this paradigm and demonstrate that excess unbound polymer during semiconductor film fabrication is not necessarily detrimental to device performance. Over 1200 TFT devices were fabricated from 30 unique polymer-sorted SWNT dispersions, prepared using two different alternating copolymers. Detailed Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) studies of the random-network semiconductor films demonstrated that a simple solvent rinse during TFT fabrication was sufficient to remove unbound polymer from the sc-SWNT films, thus eliminating laborious polymer removal before TFT fabrication. Furthermore, below a threshold polymer concentration, the presence of excess polymer during fabrication did not significantly impede TFT performance. Preeminent performance was achieved for devices prepared from native polymer-sorted SWNT dispersions containing the "original" amount of excess unbound polymer (immediately following enrichment). Lastly, we developed an open-source Machine Learning algorithm to quantitatively analyze AFM images of SWNT films for surface coverage, number of tubes, and tube alignment.
RESUMO
The large-scale enrichment of metallic carbon nanotubes is a challenging goal that has proven elusive. Selective dispersion of carbon nanotubes by specifically designed conjugated polymers is effective for isolating semiconducting species, but a comparable system does not exist for isolating metallic species. Here, we report a two-polymer system where semiconducting species are extracted from the raw HiPCO or plasma-torch nanotube starting material using an electron-rich poly(fluorene-co-carbazole) derivative, followed by isolation of the metallic species remaining in the residue using an electron-poor methylated poly(fluorene-co-pyridine) polymer. Characterization of the electronic nature of extracted samples was carried out via a combination of absorption, Raman, and fluorescence spectroscopy, as well as electrical conductivity measurements. Using this methodology, the metallic species in the sample were enriched 2-fold in comparison to the raw starting material. These results indicate that the use of electron-poor polymers is an effective strategy for the enrichment of metallic species.
RESUMO
The separation and isolation of semiconducting and metallic single-walled carbon nanotubes (SWNTs) on a large scale remains a barrier to many commercial applications. Selective extraction of semiconducting SWNTs by wrapping and dispersion with conjugated polymers has been demonstrated to be effective, but the structural parameters of conjugated polymers that dictate selectivity are poorly understood. Here, we report nanotube dispersions with a poly(fluorene-co-pyridine) copolymer and its cationic methylated derivative, and show that electron-deficient conjugated π-systems bias the dispersion selectivity toward metallic SWNTs. Differentiation of semiconducting and metallic SWNT populations was carried out by a combination of UV/Vis-NIR absorption spectroscopy, Raman spectroscopy, fluorescence spectroscopy, and electrical conductivity measurements. These results provide new insight into the rational design of conjugated polymers for the selective dispersion of metallic SWNTs.