Theoretical predictions on efficiency of bi-exciton formation and dissociation in chiral carbon nanotubes

摘要

Efficient multiple exciton generation (MEG) in chiral single-wall carbon nanotubes (SWCNTs) is present within the solar spectrum range as shown by the many-body perturbation theory calculations combined with the density functional theory simulations. To describe the impact ionization process, we calculate exciton-to-biexciton decay rates R-2 -> 1 and biexciton-to-exciton rates R-2 -> 1 in the (6,2) and (10,5) SWCNTs. Within the solar energy range, we predict R-2 -> 1 <= 10(14) s(-1), while biexciton-to-exciton recombination is weak with R-2 -> 1/R-1 -> 2 <= 10(-2). Also we calculate quantum efficiency (QE), the average number of excitons created by a single absorbed photon, for which we find QE similar or equal to 1.2-1.6, that is 20%-60%. However, MEG strength in these SWCNTs varies strongly with the excitation energy due to highly non-uniform density of states at the low energy. We hypothesize that MEG efficiency in the chiral SWCNTs can be enhanced by altering the low-energy electronic spectrum via surface functionalization, or by mixing SWCNTs of different chiralities. Published by AIP Publishing.