Halogen-promoted long single-walled carbon nanotube growth by floating catalyst chemical vapor deposition for high-performance transparent conductive films

The integration of carbon nanotube (CNT) macroscopic assemblies into advanced electronics and energy systems requires precise control over both their nanoscale structure and bulk properties. Here, we present a halogen-assisted floating catalyst chemical vapor deposition (FC-CVD) strategy that enhances the electrical conductivity of single-walled CNT (SWCNT) films through the controlled introduction of halogen-containing organic precursors. Among the additives screened, bromine (Br) most effectively reduced the sheet resistance from ∼5400 Ω/□ to 139 Ω/□ at 90% optical transmittance. Comprehensive structural characterization shows that an increase in CNT length is the primary origin of this conductivity enhancement. The use of Br additives in FC-CVD increased the CNT bundle length and the effective length by factors of 2.7 and 7.6, respectively, which markedly reduced the density of inter-tube junctions and their associated contact resistance. Other structural factors, such as chirality distribution, bundle diameter, crystallinity, and doping effects, were found to have only minor influence. These results clarify the multifaceted role of halogen species in CNT growth chemistry and highlight how nanoscale structural design can be used to optimize macroscopic CNT assemblies for high-performance electronic and energy applications.