Technical / Research - Page 113

Scientists at National Taiwan University have found a way to improve the contrast by integrating OLEDs with solar cells. Not only do solar cells positioned behind an OLED provide a contrast superior to that achieved with polarizers, but they can also recycle energy that is usually wasted.

The scientists explain that OLEDs generally consist of a reflective back electrode, organic layers, and a semi-transparent electrode for light to exit. The reflective back electrode means that the device constantly reflects light, even when the device is off, and degrades the contrast when the display is on. Previous approaches to reduce the ambient light reflection and enhance the contrast result in lost energy from both the incident photons and the stifling of some internal OLED emission.

A recent story in the journal Advanced Materials, details advances in the use of organic light-emitting diodes (OLEDs) by Ghassan Jabbour and Jian Li, with help from graduate students Evan Williams and Kirsi Haavisto, a Fulbright scholar from Finland.

These researchers have developed an organic lighting device with 100 percent internal quantum efficiency by employing newly designed host materials coupled with optimized device architecture.

There is no waste of electricity, Jabbour says. All the current you are putting into the device is being used to produce light. It's the first time something like this has been demonstrated. Nobody else has shown a 100 percent internal quantum efficiency for lighting devices using a single molecular dopant to emit white light.

Read more here (ScienceDaily) 

Cambridge Display Technology has announced that it has been awarded another grant by the UK Department of Trade and Industry (DTI). This grant will part fund a project which will be important in the field of low-cost organic electronic devices, and especially in the development of low-cost flexible displays. The total value of project is around $500k.

The project will aim to develop commercially viable computational fluid dynamic (CFD) simulation techniques to model the drying behavior of organic semiconductors. Until now, the production of working display prototypes has required the use of empirical data which is both expensive and slow to obtain. Using the new models, the development cycle time should be significantly reduced.

Universal Display Corporation and Nippon Steel Chemical today announced a new PHOLED emitter material from Universal Display, called UDC-RD39, and the exciting collaborative results of combining this new emitter material with NSCC's commercial NS11 host material.

When combined with NS11, this new bright-red PHOLED emitter, with CIE coordinates of (0.65, 0.35), exhibits a luminous efficiency of 24 candelas per Ampere (cd/A), corresponding to a 19% external quantum efficiency, at 1000 candelas per square meter (cd/m2). Under accelerated testing conditions, this new red emitter demonstrates an operating lifetime of approximately 220,000 hours, at an initial luminance of 1000 cd/m2. These dramatic performance gains represent a 60% increase in luminous efficiency and five-fold increase in lifetime, as compared to Universal Display's first-generation commercial red PHOLED emitter. As a result, Universal Display's second-generation emitter in combination with NSCC's host material may be well suited to meet the performance requirements for TV and other demanding product applications.

GE has just posted some interesting information about their OLED product research (just after the recent GE and Konica Minolta partnership announcement).

The have successfully made a 2" x 2" OLED white light source (build out of several small OLED panels).

Ron Mertens from OLED-Info.com recently had the opportunity to interview Toshiki Mizoe, overseas sales manager, Tokki Corporation. Tokki manufactures vacuum process equipment and factory automation system, and developed the first OLED mass production system in 1999, which processed both OLED / electrode material deposition and encapsulation by one system. Tokki's OLED production system has been delivered to most of small molecular OLED manufactures in Japan, Korea and Taiwan.

Q: First of all, thank you for agreeing to conduct this interview. Can you describe your production system (ELVESS)?
ELVESS is cluster tool OLED production system, and it has evaporation chambers for organic materials and metal (for cathode), and automatic encapsulation unit is connected to the system. Total system can be run for 5 to 6 days without stop, with tact time of

Solomon Systech unveiled the SSD1355 color OLED display driver with integrated controller. This device supports up to QQVGA resolution and 262k true color and has intelligent display features for applications such as mobile phones, MP3 players, portable multimedia players and digital cameras.

The SSD1355's compact die size and superfine pitch feature allow for the manufacturing of competitive COF packages to fit all popular resolutions in the color OLED market, such as 128RGB x 160, 128RGB x 128, 128RGB x 96, 128RGB x 64 and 96RGB x 96.

GE Global Research and TOKKI Corporation announced a joint agreement to develop PECVD Film Encapsulation technology and equipment for manufacturing organic electronics such as OLED displays.

The goal is to develop and demonstrate equipment that could serve as the foundation for the future manufacturing and sale of glass-based displays that are thinner in design and much lower in cost.

As part of the agreement, GE Global Research will license its patented PECVD film encapsulation process to TOKKI for use in the company's state-of-art OLED manufacturing equipment. OLED devices require a high degree of hermetic sealing or "encapsulation," since moisture and oxygen can impede the devices' functionality.

Novaled has achieved groundbreaking results in lifetime, voltage and efficiency of top emitting RGB stacks with its PIN OLED technology. Lifetimes for blue OLEDs are up to 16,000 hours, for red and green up to 100,000 hours at an initial brightness of 500 cd/m². This latest performance means that green OLED devices are now outperforming their bottom emission reference samples by a factor of 2.5. White top emission devices achieved a lifetime of 18,000 hours at a driving voltage of 3 V and a starting luminance of 1,000 cd/m².

The lowest ever reported operating voltage has been realised for green top emission OLED stacks of 2.5 V at 1,000 cd/m². At 95 cd/A, the current efficiency is even higher than for comparable bottom emission devices. These green devices are based on standard emitter material Ir(ppy)3.

Showa Denko K.K. (SDK) has made remarkable progress in its development of organic electroluminescent (organic EL) device technology based on an innovative singlelayer organic electroluminescent devices based on phosphorescent polymer materials, achieving the world's highest external quantum efficiency of 17% for green light and 16% for blue light, respectively, with durability of 350,000 hours (initial luminance: 100 cd/m2). SDK is also developing a large surface-emission panel based on this polymer technology and will build a trial volume-production line by the middle of this year. Quantum efficiency means the rate at which energy input is finally taken out as light. Theoretically, the maximum quantum efficiency for phosphorescent organic EL device is 20%.

SDK has achieved a breakthrough by developing a new copolymer - in which phosphorescent substance and other materials are mixed - realizing highest-level emissive efficiency in the industry today.



Although low-molecular-weight-compound-based organic EL devices need to be produced at under vacuum, polymer-based organic EL devices can be produced under less expensive, normal conditions. So far, problems with emissive efficiency and durability hampered commercialization efforts. With SDK's proprietary singlelayer organic electroluminescent devices based on phosphorescent polymer materials and cleaning/interface control technology, however, it is now possible to produce high-performance and stable organic EL panels. (Since an organic EL layer of less than 100 nm in thickness is sandwiched between electrodes, the cleanliness of electrode surface and work function largely influence the device performance.) SDK will further improve the technology and aim to place the new product on the market by the end of 2008.



While organic EL devices are generally developed for high-precision display applications, including mobile phones and large-screen TVs, SDK is aiming to develop advertisement and display applications, fully utilizing the advantages of high emissive efficiency, long durability and large area-emission due to the proprietary phosphorescent copolymer. SDK is planning to achieve annual sales of 10 billion from this product in 2010.