Partnership for Solid-State Lighting Report of a Workshop (2002) / Chapter Skim
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Panel III: Organic Light Emitting Diodes
Panel III: Organic Light Emitting Diodes
Pages 66-78
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From page 66... ...
(Unlike the inorganic LED demonstrated earlier, the OLEDs were safe to examine closely.) The Advantages of OLEDs The Simplicity of OLEDs He said that OLEDs got their start in display applications, where they are not only safe but have many benefits that also apply to lighting applications.
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From page 67... ...
Electronically the two materials are very similar, although there are some differences in preparation techniques. For small molecules, vacuum deposition is used for both organic thin films and the metal electrodes; the organic compounds are deposited from a heated source directly onto the substrate in a vacuum.
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From page 68... ...
The recombination of electrons and electron holes at the interface leads to a formation of excitors, or excited states, consisting of bound electrons and holes. When the excitor energy is transferred from the host material to the dopant, the dopant emits radiation in the decay process to the ground state.4 sin physics a hole (or electron hole)
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From page 69... ...
The first proof of this solution came in the late 1990s, when investigators using iridium obtained quantum efficiencies up to around 9 percent and very good efficiencies out to the fairly high brightness of 1,000 candelas per square meter. By further optimizing the matrix into which the dopants are placed, the external quantum efficiency has been raised to 15.5 percent, which is achieved by an internal quantum efficiency of 80 percent.
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From page 70... ...
Mixing Colors The blending of colors in OLEDs turns out to be manageable, with a number of strategies for mixing colors to produce white light. Dyes can be mixed in the emissive layer of the OLED to convert, in specific contexts, other colors to white, without showing significant changes in color.
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From page 71... ...
Large-Area Applications and Energy Savings OLEDs differ in applications from inorganic LEDs. Inorganic LEDs are best suited to high-brightness point sources of light, such as spotlights, traffic lights, light filaments, and projection lamps.
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From page 72... ...
These two qualities are linked: a brighter light usually has a shorter lifetime. Commercial and industrial customers demand lifetimes of at least 20,000 hours, during which the light has to retain a constant color.
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From page 73... ...
This, he said, would require the collaboration of industry, academia, and the national labs. If an effective collaboration could be devised, he said, OLEDs have a "real potential for being a very low-cost, high-efficiency replacement for fluorescent lamps" while bringing significant energy savings and environmental benefits.
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From page 74... ...
This display is essentially a white emitter with color filters. Kodak has collaborated with Sanyo to produce a passive matrix for cell phones; its emissions can be patterned with various colors that are "pleasing to the eye and easy to see." Recently Kodak demonstrated full-color active matrix displays using a technique similar to that for liquid crystal displays; the substrate was made of thinfilm transistors and each pixel had an R-G-B emitter associated with it.
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From page 75... ...
All the devices now on the market and being tested have an overly complex encapsulation system. With organic layers deposited on a glass substrate, the anode or the cathode layer is a very reactive metal, requiring a stainless steel "can," a glued perimeter seal, and a desiccant inside the seal to capture any invading moisture.
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From page 76... ...
For example, the national labs have broad expertise in lighting design and lighting engineering, with specific expertise at Pacific Northwest National Laboratory in encapsulation methods that use thin-film technology. For materials and device research, much work is being done by industry and academia; manufacturing technology requires collaboration between industry and the national labs to drive the cost of fabrication as low as possible.
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From page 77... ...
He said that Japanese firms had applied for some 8,000 patents related to OLEDs with the expectation that OLED displays would capture a significant fraction of the $50 billion display industry in the next 5 to 10 years. He said that one way to maintain leadership in OLEDs is to push the development of roll-to-roll manufacturing and flexible substrates, where the United States is the leader.
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From page 78... ...
OLEDs versus Solar Panels A questioner asked whether the lighting industry use available thin-film solar cell technology, especially for OLEDs.
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