Photocurrent Quantum Yield of Semiconducting Carbon Nanotubes: Dependence on Excitation Energy and Exciton Binding Energy

We address the dependence of the relative photocurrent quantum yield (QY) on the excitation energy and the exciton binding energy of semiconducting single-walled carbon nanotubes (s-SWNTs) having well-defined chiral indexes, by analyzing both the optical absorption and the photocurrent spectra. First, we examine the QY of a sample consisting of one sort of nanotube (such as (7,5)), which allows revealing that QY depends on the excitation energy and hence on the nature of the electronic transition. In particular, we demonstrate that the QY of the second excitonic transition (<i>E</i>₂₂) is relatively higher than that of the first excitonic transition (<i>E</i>₁₁). Then, we extend the analysis to a sample consisting of five kinds of nanotubes (namely, (7,5), (7,6), (8,6), (8,7), (9,7)), which permits demonstrating for the first time that QY increases with increasing the nanotube’s diameter and with decreasing the exciton binding energy, according to two categories known as type 1 and type 2 nanotubes. Finally, we discuss these results in the framework of the electric-field-assisted exciton dissociation model in order to gain further insight into the photocarrier generation mechanism in s-SWNTs