APPLICATIONS OF TECHNOLOGY:
- Flat panel displays
- Smart windows
- Chemical sensors
- Other applications of transparent conductive oxides (TCOs), e.g., UV blocking film, transparent window heaters
- Inexpensive, non toxic, earth-abundant material
- Simpler and less expensive to process into thin films than existing TCOs
- Low temperature processing compatible with multiple substrates
- Higher surface area than existing thin films, allowing more efficient electrochromic windows and optical sensors
Scientists at Berkeley Lab have developed a method for fabricating conductive aluminum-doped zinc oxide (AZO) nanocrystals that provide a lower cost, less toxic, earth-abundant alternative to the widely used transparent conductive oxide (TCO) indium tin oxide while offering comparable optical and electronic properties. TCOs are used in devices such as flat screen displays, photovoltaic cells, photochromic windows, chemical sensors, and biosensors.
The optoelectronic properties of AZO nanocrystals can be tuned by controlling their aluminum content. Since they are produced as a colloidal printable nanoink, they can be deposited at room temperature on substrates by methods such as spin coating and drop casting, which are less expensive and more convenient than existing methods for producing TCO thin films (e.g., magnetron sputtering, pulsed laser deposition). Moreover, their annealing temperatures of 250°C or less are compatible with multiple substrates, including plastics and polymers. The nanocrystals also maintain their crystalline structure and high surface area after deposition, which will allow for improved efficiency of photochromic windows and lower detection limits for chemical sensors.
The scientists fabricated the nanocrystals by injecting a zinc precursor, aluminum precursor, amine, and fatty acid into solvents. They were able to precisely control the size of the crystals (5 to 30 nm) and the Al-doping content (0.5 to 8.0%). Analysis of transmission electron microscope images and x-ray diffraction showed a high degree of crystallinity. Additional spectroscopy evidenced transparency in the visible range and tunable IR reflectance. Thin films made from the nanocrystals were highly uniform, transparent in the visible range, and had an electrical conductivity resembling that of other nanocrystalline thin films.
Conventional TCO thin films are costly because their production and deposition often require ultrahigh-vacuum chambers. In addition, their processing and annealing temperatures, well above 500°C, make them incompatible with heat-sensitive substrates. The Berkeley Lab nanocrystals overcome these limitations while maintaining the benefits of state-of-the-art TCOs and providing a high surface area.
DEVELOPMENT STAGE: Bench scale demonstration.
STATUS: Patent pending. Available for licensing or collaborative research.
FOR MORE INFORMATION:
Buonsanti, R., Llordes, A., Aloni, S., Helms, B.A., Milliron, D.J. "Tunable Infrared Absorption and Visible Transparency of Colloidal Aluminum-Doped Zinc Oxide Nanocrystals," NanoLetters, Oct. 4, 2011 (web).
SEE THESE OTHER BERKELEY LAB TECHNOLOGIES IN THIS FIELD:Branched 3-D Inorganic Nanocrystals for Biological Imaging and Electronics Applications, IB-1773
REFERENCE NUMBER: IB-2967