Photocurrent Generation from Light Absorption by Semiconducting Single Walled Carbon Nanotubes

We demonstrate significant advances in the fundamental understanding of charge generation in semiconducting single walled carbon nanotube (s-SWCNT) hybrid systems. By developing preparation schemes based on the dispersion selectivity of poly(9,9 dioctylfluorenyl 2,7-diyl) and related copolymers, we accessed solution-based populations of s-SWCNTs in purities high enough to study the intrinsic photophysics of s-SWCNT light absorbers in cast films. Using these films we demonstrate that little-to-no charge is generated in optically excited, films of polymer-wrapped s-SWCNTs. More importantly, we demonstrate efficient charge generation via the dissociation of photogenerated excitons on s-SWCNTs at type-II electronic heterojunctions between s-SWCNTs and charge accepting semiconductors, when electronic offsets exceed the exciton binding energy. We demonstrate exciton dissociation via electron transfer to C60 and photocurrent generation in quantum efficiencies exceeding 85%, and experimentally identify a s-SWCNT diameter cutoff around 1.0nm above which the efficiency of photogenerated electron transfer to C60 quickly falls off. We use the high efficiency of exciton dissociation at this interface and s-SWCNT samples highly enriched in a single chiral species to measure photocurrent collection from excitons optically excited into excitonic manifolds above the groundstate in equivalent efficiencies as excitons directly excited into the groundstate. We extend our understanding of photocurrent generation in s-SWCNT/C60 heterojunctions, in collaboration with scientists at the National Renewable Energy Laboratory (NREL) and reveal the competition between `fast' recombination processes intrinsic to the s-SWCNT films with time constants of order 10ns and much slower recombination across the heterointerface, with time constants of order 850 ns. We study the effect of residual PFO on photocurrent generation, and trace s-SWCNT film thickness trends in photocurrent generation efficiency back to exciton diffusion and the percolation of individual s-SWCNTs within the film. We demonstrate photovoltaic power conversion of near infrared light via s-SWCNT exciton dissociation variously throughout the dissertation, and close with an outlook on the emergent field of s-SWCNT based photovoltaics.