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In 1989, researchers at the Cambridge University Cavendish Laboratory found that passing an electric current through certain polymers made them emit light. CDT was formed in 1992 to commercialise the technology that evolved from this discovery. CDT owns the fundamental intellectual property and expertise in light-emitting polymers (P-OLEDs).

P-OLED displays are made by applying a thin film of light-emitting polymer onto a glass or plastic substrate coated with a transparent electrode. A metal electrode is sputtered or evaporated on top of the polymer. Application of an electric field between these two electrodes results in emission of light from the polymer. When a current is applied, electrons from the cathode migrate through the cell and meet positive ‘holes’ migrating from the anode. When they meet, they form so-called excitons, and as electrons relax, energy is released as light.
See also: Introduction to P-OLEDs.

Polymers are long chains of organic molecules. P-OLEDs are special classes of polymer which have been found to emit light when stimulated electrically. P-OLEDs can be formulated to generate specific colours of light and have properties that are compatible with both the intended application as well as the process for deposition. There are currently two major families of P-OLED organic polymers: poly p-phenylenevinylene (PPV) and polyfluorene (PF).

Because P-OLEDs emit their own light, they are brighter, clearer, and have a virtually unlimited viewing angle. Their high contrast and wide dynamic brightness capabilities make them a better solution for night-time and daylight use. P-OLEDs also have a very fast image refresh rate that is maintained at low temperature, and are ideal for full colour video in TV, internet devices, PDAs and other ‘smart’ personal display products. Because P-OLEDs do not require a power-hungry backlight, they are energy efficient and are thinner and lighter weight.

Unfortunately, as with many relatively new technologies, a profusion of terms has developed world-wide. You’ll find PLED and P-OLED used widely to mean organic light emitting diodes based on organic polymers, although OEL is also seen particularly in Asia. Please see our Glossary for more information.

Typically polymers have only two end groups, one at each end of the polymer chain. Branching can be introduced into the polymer along the polymer backbone, thereby increasing the number of end groups present. Branching can be important in terms of cross-linking and in the formation of three- dimensional networks or films. At high levels of branching, hyper branched or star-like polymers can be made. Dendrimers are similar to hyper-branched polymers. They possess repeating units in their structure that radiate from a central core.

Dendrimers are usually of a precise molecular weight, i.e. they are monodispersed. The chains radiating from the central core are usually referred to as dendrons. Looking from the exterior of the molecule, a dendrimer appears spherical with the end groups of each dendron lying on the surface of the sphere. These groups can be used in further reactions, such as cross linking, or may be used to modify the surface properties of the material, e.g. to make it more or less hydrophilic. Dendrimers have an extremely high concentration of functional groups or functionality for their molecular weight or volume.

Power consumption depends on the nature of the image displayed but for general use, P-OLED based displays are expected to consume less power than equivalent LCD or plasma products.

CDT is a wholly owned subsidiary of Sumitomo Chemical Company. CDT Ltd is a legal entity and will continue to pursue its licensing and technical services business model.

CDT’s business model is based on licensing, technology development and technology transfer. CDT develops technology related to P-OLED applications, including displays, lighting and organic semiconductors.

CDT works with potential licensees and development partners to evaluate and demonstrate the benefits of P-OLED technology. In some cases, this collaborative approach will take the form of a Joint Development Agreement (JDA).

P-OLED technology has the major advantage of being solution processable. That is to say, P-OLED devices can be manufactured using printing techniques such as inkjet or roll printing as part of the manufacturing process. As devices can be manufactured on flexible plastic substrates, in future we should see displays that have non-planar shapes.

Much of the clean room equipment required to manufactured P-OLEDs already exists in an LCD plant. In fact the manufacturing process for P-OLEDs offers simpler processes and potential cost savings compared with LCD: they do not have backlights or colour filters and need fewer process steps. The key difference is that a P-OLED display can be ‘printed’ using conventional ink jet printing technology.

Costs to manufacture P-OLED displays, when compared with LCDs of comparable volume and maturity of production tools and processes, are expected to be between 30% and 55% lower depending on display size, due to the simpler bill of materials and elimination of the backlight and colour filters.

P-OLED has four key applications:

• Large emissive panels that can be used in lighting applications, replacing incandescent and fluorescent bulbs.
• Low information content displays where inorganic LEDs are currently used: video, hi-fi, shaver, watch etc.
• Displacement of cathode ray tube (CRT) or LCD displays in applications such as: mobile phones, personal digital assistants (PDAs), computer monitors and televisions.
• New display applications for which P-OLED characteristics make it uniquely suited, e.g. automotive instrument panel, dynamic advertising applications, graphical signs for point of sale or purchase, electromechanical signage, bio-medical testing.

Not directly. CDT has a broad, global plan for developing polymer technology to a stable and mature commercial level and speeding its transfer into manufacturing for a wide range of market applications. The scope of CDT activities includes basic research in polymer materials and synthesis, and development of material systems, device architectures and processes. Collaboration, joint venture, and licensing are the business models CDT is employing with strategic partners around the world to ensure successful P-OLED commercialisation.

You can also follow up on our Technical References to published works. If you’d like to contact us for more information, we’d be delighted to hear from you.