Fluorination of single-walled carbon nanotubes and their application in organic photovoltaic cells as an electron acceptor

A technique for increasing the degree of dispergation of TUBALL (OCSiAl) single-walled carbon nanotubes (SWCNTs) and for obtaining individual nanotubes was developed. A combination of steps including preliminary purification of the starting SWCNTs from residues of iron-containing catalyst, ultrasonic dispergation of SWCNTs, chemical shortening of SWCNTs, mild fluorination of SWCNTs in BrF3 vapors, centrifugation of a dispersion of SWCNTs in o-dichlorobenzene, and isolation of individual SWCNTs during supernatant filtration was used. This procedure led to a decrease in the average length of SWCNTs and a noticeable decrease in the diameter of their bundles. A considerable portion of a dispersion of SWCNTs separated in this manner consisted of individual nanotubes with diameters of 1-2 nm, in addition, there were bundles with diameters of up to 6 nm. This technique made it possible to obtain photovoltaic cells based on a composite of a conjugated polymer of poly-3-hexylthiophene (P3HT) and fluorinated SWCNTs with a reproducible photovoltaic effect. The energy of the boundary LUMO of fluorinated SWCNTs was determined to be equal to -4.3 eV by cyclic voltammetry. This is suitable for light-induced electron transfer from P3HT and most other donor polymers to fluorinated SWCNTs.