Diffusion Assisted Photoexcitation Transfer in Coupled Semiconducting Carbon Nanotube Thin Films

TitleDiffusion Assisted Photoexcitation Transfer in Coupled Semiconducting Carbon Nanotube Thin Films
Publication TypeJournal Article
Year of Publication2014
AuthorsGrechko M, Ye Y, Mehlenbacher RD, McDonough TJ, Wu M-Y, Jacobberger RM, Arnold MS, Zanni MT
Secondary TitleACS Nano
Date Published05/2014

We utilize femtosecond transient absorption spectroscopy to study dynamics of photoexcitation migration in films of semiconducting single-wall carbon nanotubes. Films of nanotubes in close contact enable energy migration such as needed in photovoltaic and electroluminescent devices. Two types of films composed of nanotube fibers are utilized in this study: densely packed and very porous. By comparing exciton kinetics in these films we characterize excitation transfer between carbon nanotubes inside fibers versus between fibers. We find that intra-fiber transfer takes place in both types of films, whereas inter-fiber transfer is greatly suppressed in the porous one. Using films with different nanotube composition, we are able to test several models of exciton transfer. The data is inconsistent with models that rely on through-space inter-fiber energy transfer. A model that fits the experimental results well postulates that inter-fiber transfer occurs only at intersections between fibers and the excitons reach the intersections by diffusing along the long-axis of the tubes. We find that time constants for the inter- and intra-fiber transfers are 0.2 - 0.4 ps and 7 ps, respectively. In total, hopping between fibers accounts for about 60% of all exciton downhill transfer prior to 4 ps in the dense film. The results are discussed with regards to transmission electron micrographs of the films. This study provides a rigorous analysis of the photophysics in this new class of promising materials for photovoltaics and other technologies.

Short TitleACS Nano