Direct Tracking of Ultrafast Carrier Motion Dynamics in Semiconducting Single-Wall Carbon Nanotubes

摘要

An Ultrafast all-optical electric field strength measurement technique based on the electric-field-induced second harmonic generation together with conventional transient photocurrent measurements has been applied for the direct tracking of carrier separation and motion dynamics in semiconducting single-wall carbon nanotubes (SWNTs). Thin films of (6,5)-SWNT-enriched samples were prepared on combs of interdigitated electrodes with different concentrations of fullerene derivative phenyl-C-61-butyric acid methyl ester (PCBM) serving as an electron acceptor. Neutral delocalized excitons photogenerated in the samples with high PCBM concentration were found to form localized charge-transfer (CT) states within less than 1 ps with the electron transferred to the PCBM and a hole remaining on the SWNT. The hole's drift along the length of individual nanotubes was found to take similar to 200-1000 ps and is most likely limited by dissociation of the CT states rather than by the hole's mobility. A fraction of about (30-50)% of generated charge carriers was found to recombine within 3.6 ns measurement interval.