Research Terms
This conjugated polymer ensures reliable non-covalent interactions between secondary materials and carbon nanotube films without degrading the conductivity. Graphene or carbon nanotube films can produce robust, flexible and transparent electrodes, supporting the design of a broad range of devices including electrochromic windows, capacitors, super-capacitors, light emitting diodes, light emitting transistors, electrostrictive devices, and more. To perform optimally, some secondary material must be electrically coupled to the graphene or nanotube film. However, adhesion to such secondary materials is typically very weak for available graphene and carbon nanotube surfaces because they are chemically self-satisfied , or Teflon-like, resulting in material separation. This problem is particularly severe in flexible film applications because strain can cause delamination of the secondary material from the graphene or carbon nanotube surface, severely degrading the electrical contact and impairing the performance of the device. Conventional solutions to overcome this problem include attaching chemical anchors along the nanotube sidewalls that bond with the secondary material. Unfortunately, such covalent attachments degrades their intrinsic electrical conductivity.
Researchers at the University of Florida have developed a synthesized electroactive polymer backbone, coupled along its length to multiple flexible linkers that bind non-covalently to a graphene or carbon nanotube sidewall. Because the polymer backbone is itself electroactive, and molecularly thin, the graphene or carbon nanotubes attain good electrical coupling to the secondary material, while also being strongly bonded to it, even when strained.
Conducting polymers that bind to graphene or nanotubes to allow their strong association with secondary materials, avoiding their delamination (even under large strains) without impeding the electrical contact between the graphene or carbon nanotubes and the secondary material
This conducting polymer consists of two components: a conjugated polymer backbone and polymeric aromatic hydrocarbon chains. The conjugated polymer backbone contains delocalized electrons, which flow throughout the entire composite whenever an electric field is applied. The hanging hydrocarbon chains have a functional group attached, which can vary per conducting polymer. With multiple functional groups included per polymer segment, non-covalent interactions are secured, thus creating stable composites of carbon nanotubes or other graphene-based materials.
Patent Issued: US 8,961,830
This carbon nanotube-semiconductor junction allows for performance control via electronic gating, enhancing the efficiency of Schottky diode solar cells. Solar power is a rapidly growing industry with a promising future for continued growth. More than 20,000 megawatts of cumulative solar electric capacity is operating in the United States, enough to power more than 4 million American homes. Researchers at the University of Florida have developed a Schottky diode solar cell that integrates carbon nanotube-semiconductor junctions and electronic gating for substantial enhancement in the power conversion efficiency. The solution processing for this Schottky diode solar cell is less expensive to manufacture than available solar cells, allowing for a more cost-effective commercial solar cell.
Efficient, high performance Schottky junction solar cells
These solar cells use a carbon nanotube-semiconductor junction and electronic gate-induced modulation of the contact barriers between the carbon nanotubes and the organic semiconductor layer to maximize the power conversion efficiency of the cell. The electronic gating modifies the interface dipole at the junction between the nanotube and semiconductor to reduce barriers to electronic transfer across the junction. The electronic gating also contributes to the electrical field across the depletion layer, which enhances the efficiency and boosts the power generation capabilities of the solar cells. Efficiencies of 15 percent in non-optimized cells have been demonstrated, comparable to commercially available crystalline silicone powered cells. The solution processing involved in producing the solar cells is less expensive to manufacture than currently available solar cells, providing a more cost-effective alternative to commercial solar cells.
These carbon nanotube films exhibit high porosity and surface area to create 3D electrical contact interfaces for electrodes, improving the performance of a range of electrical devices and processes. Electrodes, which send current through non-metal materials, are integral to a wide variety of applications including welding, grounding, medical testing, and chemical processing. The electrochemical instrument market alone will reach a value of $2.2 billion in 2019. Electrodes largely rely on planar 2D interfaces between the electrode and contact material. 3D electrical contacts between electrodes and materials could benefit numerous applications by increasing conductivity through greater surface area. While some available carbon nanotube films achieve this to a certain extent, the area increase is not significant enough due to the low porosity of the films.
Researchers at the University of Florida have developed a process to fabricate highly porous, electrically conductive, single-wall carbon nanotube (SWNT) films for use as electrodes that establish high surface area 3D contact. This type of contact improves the performance of a range of electrical devices and processes such as electrochemical hydrogen production, solar cells, and electroluminescent devices.
Electrodes with carbon nanotube electrical contacts that improve device and process performance
These fabricated carbon nanotube films feature high porosity and increased electrical contact surface area. During the fabrication process, a porous membrane filters out carbon nanotubes and sacrificial nanoparticles from a surfactant suspension. These nanotubes and nanoparticles accumulate on the surface of the membrane, forming a film. Next, the membrane undergoes washing to remove the surfactant and drying to consolidate the film. Dissolution, evaporation, oxidation, pyrolysis or etching removes the sacrificial particles from the film to increase its porosity. After transferring the film to the final substrate, a solvent dissolves the membrane, leaving only the carbon nanotube film behind. The film created from this process is highly porous because of the use and removal of the sacrificial nanoparticles. These pores create a much greater surface contact area, increasing the local field strength of the electrode while keeping the resistivity low. This improved field strength can increase electron gathering for solar cells, as well as improve local conductivity and reactivity for more-efficient electroluminescent devices and electrochemical processing respectively.
