Comparison of Cluster Formation, Film Structure, Microwave Conductivity, and Photoelectrochemical Properties of Composites Consisting of Single-Walled Carbon Nanotubes with C₆₀, C₇₀, and C₈₄

The cluster formation, electrophoretically deposited film structures, microwave conductivity, and photoelectrochemical properties of the composites consisting of single-walled carbon nanotube (SWNT) with C 60, C 70, or C 84 have been systematically compared for the first time. In an ortho -dichlorobenzene (ODCB)−acetonitrile mixture, the higher fullerenes (i.e., C 70 and C 84 ) were found to form single composite clusters exclusively with highly soluble SWNT bearing bulky swallow-tailed substituents (f-SWNT). These are in marked contrast with the unselective formation of three different clusters in the C 60 −f-SWNT composites. Electrophoretic deposition of the composite clusters yielded the corresponding films on nanostructured SnO 2 electrodes. The microwave conductivity measurements revealed the occurrence of electron transfer from C 70 to f-SWNT, followed by electron transportation through f-SWNT, in addition to electron hopping through C 70 molecule arrays due to the alignment of C 70 on the sidewalls of f-SWNT in the C 70 −f-SWNT film. The C 70 −f-SWNT photoelectrochemical device exhibited higher incident photon-to-current efficiency (IPCE) value (26% at 400 nm) than the C 60 −f-SWNT device (18%). The higher IPCE value results from selective formation of the single composite film, in which the SWNT network is covered with C 70 molecules, and the high electron mobility (2.4 cm 2 V −1 s −1 ) through the C 70 −SWNT network. In contrast, the C 84 −f-SWNT photoelectrochemical device revealed poor photocurrent generation (4.8%) owing to the inefficient electron injection from C 84 radical anion (C 84 /C 84 •− ≈ 0.0 V vs NHE) to the SnO 2 electrode ( E CB = 0 V vs NHE) directly or indirectly despite the exclusive formation of the single composite clusters. Thus, the results obtained here will provide valuable information on the design of molecular devices based on carbon nanotubes and fullerenes.