Ito Replacement To Impact Oled Devices

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ITO Replacement to Impact OLED Devices       In spite of the worldwide recession, interest remains strong in OLEDs. Mobile phone manufacturers continue to shift from LCD panels in favor of OLED panels for their products. Pent up consumer demand for thin, high-quality OLED televisions and computer monitors make every mention of commercial production plans (or conjecture about production plans) a lead story in display industry news outlets. Recent reports call for large format OLED products from LG, Panasonic, and Samsung as well as a larger OLED TV model from Sony by next year, with some products appearing as early as the end of this year. Not all the interest is focused on pixilated displays, either. Architectural lighting continues to be the application most likely to drive the next advance in production volume. For example, the National Energy Testing Laboratory of the U.S. Department of Energy announced funding of 16 solid-state lighting projects, six of which are based on OLED technology. Recipients include QD Vision, Inc., University of Florida, DuPont Displays, Kodak, and Universal Display Corporation (UDC). As a result, the progress in OLED technology shows no signs of slowing down. These advances have significant implications for the OLED materials markets. One of the most intriguing sets of advances is the use of silver instead of ITO in device anodes. Silver Lining While research continues on materials that make up the organic stack of OLED devices--the major contributor to materials cost--there's also room for improvement for the more mundane materials such as the electrodes. In particular, there is considerable amount of research into finding an alternativ e to indium tin oxide (ITO)--a trend that will affect many industries, but one of especial interest for OLED panels. Not only is ITO's pricing and supply subject to wild fluctuations, it is also not an optimal material. ITO does not fare well in flexible applications, and can have planarization issues that can negativ ely affect the extremely thin layers used in an OLED stack. Spikes in the ITO layer can reach through subsequent layers and create shorts or cause adverse reactions with the emissive layer materials.

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One of the most promising approaches is to eliminate the ITO altogether. A number of different researchers have explored using silver as an alternative. A European consortium including Agfa Materials, Philips Research, and the Holst Centre have demonstrated an OLED lighting tile that does not use ITO. The anode conductor relies primarily on PEDOT:PSS as a conductor, using Agfa's Orgacon G4 PEDOT:PSS. This was a new formulation that was designed specifically for a high level of transparency and high conductiv ity. The consortium made a 12 by 12 cm white OLED lighting tile by inkjet printing (instead of the traditional photolithography processes that require several steps) a grid of metal shunting using silver nanoparticle-based ink onto a PEN plastic substrate. PEDOT:PSS was used as the anode and hole injection layer. The research was funded in part by the EU's FP7 Fast2Light project. In addition to eliminating ITO, the process also eliminates the need for lithography and other manufacturing steps, simplifying production and reducing costs. The result is a lighting tile that can be produced using roll-to-roll manufacturing. Other companies are also exploring approaches that involve silver as an alternative to ITO in OLED devices. Dai Nippon Printing (DNP) announced that it has developed a process that allows roll-toroll printing of a mesh made of silver nanowires that serve as an electrical grid. It is more conductive than ITO, and more flexible. DNP claims that the material has a low resistance of 0.1 &/cm2 (ohms per square centimeter). The printing process does not require photolithography to create the pattern, and the wires are so fine that the resulting film is highly transparent. The company notes that the metal grid may also offer the side benefit of blocking some electromagnetic emissions from electronics devices, as adjusting the grid size can tune the layer to block certain radio frequencies. DNP expects samples to be available in May 2009 with full production scheduled for the fall of 2009. Fujifilm has demonstrated a similar wire mesh coating using silver nanowires on a PET substrate. The sheet resistance can be adjusted by modifying the diameter and pattern of the wires; the company claims that a range of about 0.2 to 3,000 &/cm2. The low end of this range is about 10 to 40 times lower than is typical for an ITO layer.

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In a demonstration, the substrate was bent around a 4 mm cylinder without damaging the conductive layer. The demonstrated material was 80-percent transparent, but according to company representatives, the process can be used to create films with transparencies as high as 89 percent. The mesh is produced using a coating process that is designed to work with roll-to-roll processing, and is expected to cost less than ITO films. Production is scheduled for late summer or early fall of 2009. The Outlook for OLED The current state of the world economy makes immediate success for large format OLED displays such as televisions and computer monitors unlikely in the near term. Mobile device sales are also off dramatically--down 20 percent to almost 50 percent for the first quarter of 2009 according to some sources--but are likely to recover fairly quickly now that inventories have been reduced to more manageable levels. The prospects for OLED lighting do not appear to be as negatively impacted by the current economic situation as the other applications, in part due to various governments providing funding for research and development, often as part of economic stimulus and energy-savings programs. As a result, there will be both a push in the form of government funding and a pull from consumer demand for more efficient and environmentally friendly lighting. At the time of writing this article, the price of crude oil and other energy forms is low, but there are many indications that those prices will start rising again soon. Higher energy prices will further increase the demand for efficient and long-lived, solid-state lighting solutions, including OLED. These novel designs and materials that eliminate the need for ITO are still unproven. While they show promise in terms of lowering production costs and possibly material costs as well, we won't know their true value until they start to reach the end user in significant quantities. Only then will we be able to make an accurate assessment of whether or not the promised cost savings can be realized. In addition, while these silver conductor solutions may offer additional benefits such as flexibility and durability, it remains to be seen whether these attributes will translate into features that will increase the end products' appeal to consumers. One major advantage for these ITO-replacement strategies is that they are not solely dependent on the OLED industry for their success. The same technology can serve the needs of other

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markets, including touch screens, LCD displays, solar cells, and printable electronics. If they gain a toehold in any of these or other similar industries, they can help leverage the economies of scale in production that will help them compete more effectiv ely in the remaining markets, including OLED.  

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