In November, DuPont announced that it had signed a licensing agreement for its proprietary solution-based printing technology to be used by a leading Asian manufacturer to make large AMOLED televisions. At press time, DuPont was – at the manufacturer's request – not at liberty to reveal the name of the manufacturer. Since Asian TV makers with a vested interest in OLEDs can be counted on the fingers of one hand, the pool of possible partners is small indeed, with online speculation leaning in the direction of Samsung or LG. Nothing is certain until the partnership is made public, which, according to Bill Feehery, Global Business Director for Dupont, will definitely happen on an as-yet undisclosed date.
DuPont's technology is of particular interest because it allows the OLED materials to be spray-printed on a backplane using a superfast multi-nozzle technique. The printer, developed by DuPoint in conjunction with Dai Nippon Screen, uses a continuous spray of ink rather than droplets and coats the substrate at rates of 4–5 m/sec. According to DuPont, a Gen 4 OLED display can be printed in about 2 minutes.
The company has been working on this technique for several years. "We've had many iterations," says Feehery. "It wasn't easy." The key challenges were improving the performance of the material, including its color and efficiency, and being able to print at a high yield without mura. The key to scaling up to Gen 4 was using multiple nozzles, notes Feehery.
This announcement would seem to indicate that OLED TVs are inching closer to commercial reality, although "We're only a piece of the OLED puzzle," Feehery is quick to point out. Other developers have had to solve issues such as reliable encapsulation and the ability to make backplanes at a larger size. And this has been happening. Feehery notes that even if DuPont had had the process ready 5 years ago, there would not have been a market for it because the other pieces of the OLED equation were not ready. Are they ready now? We'll have to wait just a bit longer to find out.
For more background on this technology, see the article from DuPont Displays, "Clearing the Road to Mass Production of OLED Television, in the October 2011 issue of Information Display.
– Jenny Donelan
Part I of our Solid-State-Lighting Update in the October issue of ID magazine looked at OLED-based developments from European companies such as BASF, Novaled, and OSRAM, as well as activities conducted by OLED research groups including the OLED100.eu consortium (which recently concluded its research in Q3 '11 on schedule) and the TOPAS (Thousand lumen Organic Phosphorescent devices for Applications in lighting Systems) 2012 research project. Two other companies involved in the European solid-state-lighting push include AIXTRON and Nanaco.
AIXTRON
"The special features of OLED solid-state lighting, such as the potential for free-form and/or transparent-area light sources, appeal to many designers and allow for novel architectural concepts," says Juergen Kreis, Senior Department Manager for Business Development at AIXTRON, a leading provider of deposition equipment to the semiconductor industry. "Also," says Kreis, "the fact that OLEDs already are luminaires and only need a minimum of additional packaging makes this technology especially interesting."
At this moment, he notes, manufacturing costs and the respective pricing of OLED devices are not competitive with other technologies such as inorganic LEDs. Therefore, the OLED-based devices that are currently being produced still serve mostly as proof-of-principle or are designed for niche markets such as high-end interior design.
Says Kreis, "Technically, the so-far-dominant vacuum thermal evaporation (VTE) seems to create some limitations when it comes to scaling up to larger substrate sizes." Some of these challenges, he continues, such as efficient material use, high deposition rates and throughput, avoiding parasitic material deposition in the process chamber, and minimizing thermal stress to the organic material, are being addressed by AIXTRON's OVPD technology. The OVPD system uses AIXTRON's proprietary Close Coupled Showerhead (CCS) technology to ensure homogenous material distribution, uniform film thicknesses, and efficient utilization of the organic materials.
Exposing organic materials to elevated temperatures over a long period of time usually speeds their degradation and can render sensitive materials unusable in processes for larger substrates. In conventional VTE systems, scaled-up solutions also require the scaling up of the respective crucibles, which, in turn, keeps larger amounts of materials at elevated temperatures for a considerable period of time.
AIXTRON's novel STEx source principle addresses this hurdle by enabling on-demand evaporation of materials (bulk material is kept under room temperature), and at the same time providing high deposition rates, which then allows for short cycle times and high throughput.
Says Kreis, "For white OLEDs, efficient blue emitters still are a challenge with respect to lifetime. It should be noted, however, that here (as well as in many other fields) tremendous progress can be seen from the major material makers." Support programs such as those funded by the EU, he notes, will, for the near future, be necessary to help companies endure the incremental investments necessary to make this technology a success.
Nanaco
Quantum dots, semiconductor nanoparticles between 10 and 100 atoms in width, hold promise for solid-state-lighting applications due to their unique electro-optical characteristics. These include the ability to emit light of a very specific wavelength depending on the size of the dot. However, to date the challenges involved in bringing this technology to market include power efficiency, cost to manufacture, and scalability.
One company that is firmly vested in quantum-dot technology for LEDs and other applications, and says that it is currently capable of producing quantum dots on a large scale, is the UK-based Nanaco Technologies. "Nanoco has been working with lighting manufacturers to help them develop LED lighting incorporating its quantum-dot technology," says Nanoco representative Mark Court. Last August, according to Court, the company signed a joint development agreement with one of the world's largest lighting companies (the name can not be divulged) with the aim of creating LED lighting with superior color performance.
Nanoco believes that its quantum-dot technology has the potential to bolster the widespread use of solid-state lighting in commercial, residential, and other settings and is therefore a key area of Nanoco's R&D activities. According to Court, the company has already developed a range of trial units that combine the company's red quantum dots with blue LEDs to create a "warm" white light with a high color-rendering index.
When blue light from an LED passes through red quantum dots, the light is re-emitted as red light. Similarly, green quantum dots can be combined with a blue LED to achieve green light. A blue LED with red and green quantum dots produces what appears to the human eye as white light. This white light can be in an almost infinitely variable range of shades, dependent on the particular size and combination of red and green quantum dots.
According to Court, Nanoco can control the size of the quantum dots to control the shade of light emitted and should therefore be able to develop LED lighting with the required characteristics for the home, office, and elsewhere. Nanoco is also working with the liquid-crystal-display (LCD) industry to combine quantum dots with LEDs for TV backlighting applications.