(623a) Photovoltaic Electrochemical Optical Rectennas of Carbon Nanotubes with Self-Assembled Monolayers

Carbon nanotubes (CNT) and CNT-gold hybrid nanostructures are shown to produce rectified photocurrents without pre-bias when illuminated in the presence of aqueous electrolytes containing anionic surfactants. Graphite nanoplatelets, multi-wall carbon nanotube mats, single-wall carbon nanotube (SWNT) arrays and carbon black-loaded polymer all display this novel photovoltaic effect, and share a unique isolated photocurrent peak at ~300 nm. This feature apparently originates with their shared π-plasmon absorption. Rectified photocurrents are obtained only in the presence of anionic surfactants known to form self-assembled monolayers on graphitic surfaces. Carbon nanotube electrodes also produce minor photocurrents in the near infra-red. When coated with 5 nm of gold, single-walled carbon nanotube arrays generate similar photocurrents when treated with thiol-terminated anionic surfactant molecules. The Au-SWNT composite nanostructure displays a broad photocurrent spectrum spanning the entire visible region, along with a pronounced peak at ~400 nm. These features appear to arise from photoabsorption by gold nanorod plasmon hybridized with SWNT π-plasmons. A model explaining these results based on hot carriers traversing a rectifying tunnel barrier is presented and discussed. This mechanism is consonant with the concept of an optical rectifying antenna (rectenna), and could enable development of high efficiency photodetectors, photovoltaics and photochemical converters.