Carrier photogeneration, drift and recombination in a semiconducting carbon nanotube network

Abstract

Charge carrier photogeneration, drift and recombination in thin film networks of polymer-wrapped (6,5)-single-wall carbon nanotubes (SWNTs) blended with phenyl-C61-butyric acid methyl ester (PCBM) have been investigated by using transient photocurrent and time-delayed collection field (TDCF) techniques. Three distinct transient photocurrent components on the nano- and microsecond timescales have been identified. We attribute the dominant (>50% of total extracted charge) ultrashort photocurrent component with a decay time below our experimental time-resolution of 2 ns to the intratube hole motion. The second component on the few microsecond timescale is attributed to the intertube hole transfer, while the slowest component is assigned to the electron drift within the PCBM phase. The hole drift distance appears to be limited by gaps in the nanotube percolation network rather than by hole trapping or recombination. Photocurrent saturation was observed when excitation densities reached more than one charge pair per nanotube; we attribute this to the local electric field screening.

Electronic and Ionic Electric Field Screening and Persistent Built‐In Electric Field in Carbon Nanotube/PCBM Films

“…This decay phase closely resembles the recombination kinetics of photogenerated charge carriers determined by the time‐delayed collection field (TDCF) technique reported in ref. . Therefore, this phase should be attributed to the motion of equilibrium charge carriers present in a SWCNT layer.…”

“…Application of these nanomaterials in electronic devices requires clear understanding of their various physical properties, especially charge transport properties, which are particularly important for any electronic material. Charge transport through the bundles of SWCNTs as well as its dependence on the temperature, doping, and intertube interactions have been addressed in a number of publications. Charge carrier photogeneration and their transport through the SWCNT network can be considered as very fast or ultrafast process .…”

“…Charge transport through the bundles of SWCNTs as well as its dependence on the temperature, doping, and intertube interactions have been addressed in a number of publications. Charge carrier photogeneration and their transport through the SWCNT network can be considered as very fast or ultrafast process . Intratube charge carrier mobility reaches thousands of cm 2 (V s) −1 , which makes them interesting for fast electronics.…”

“…However, charge carrier motion in carbon nanotube films is extremely dispersive. The intratube carrier transport takes place on a picosecond timescale, while intertube carrier jumps are much slower occurring on a timescale of tens of microseconds . Gadermaier et al.…”

“…PCBM is an efficient electron acceptor widely used in organic solar cells. PCBM also strongly enhances the photoconductivity of SWCNT films by accepting electrons from the photoexcited SWCNT . Such SWCNT/PCBM blend has been tested for application as active solar cell material .…”