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Miniscule amounts of impurities in vacuum reduce OLED lifetime

Miniscule amounts of impurities in vacuum reduce OLED lifetime
Photo courtesy: Hiroshi Fujimoto and William J. Potscavage, Jr

By BizLED Bureau

May 25, 2017: To convert from electricity into light, OLEDs use a number of organic layers, which are fabricated by heating source materials in vacuum, so that they evaporate and deposit onto a lower temperature substrate.

Researchers are still trying to find out why OLEDs degrade and lose brightness over time. However, a new research by Kyushu University shows that miniscule amounts of impurities in vacuum get incorporated into the OLEDs during the fabrication process that lead to variations in lifespan.

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Besides organic impurities, water in the vacuum chamber also decreases lifetime of OLEDs, and leads to a correlation between device fabrication time and lifetime.

How to avoid these impurities

According to Hiroshi Fujimoto, chief researcher at Fukuoka i3-Center for Organic Photonics and Electronics Research (i3-OPERA) and visiting associate professor of Kyushu University, these impurities can be avoided by cutting down the time of the fabrication process by keeping the OLEDs for lesser time in the deposition chamber. This will reduce impurities and increase lifetime of OLEDs.

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The researchers found that these impurities have come from the sources that include deposited materials and plasticizers from the chamber components. This means that the impurities floating in the vacuum chamber impact the lifetime values and reproducibility of OLEDs.

“Although we often idealize vacuums as being clean environments, we detected many impurities floating in the vacuum even when the deposition chamber is at room temperature,” says Hiroshi Fujimoto.

The researchers came to the conclusion that OLEDs can have better reproducible and long lifetime if they include a vacuum-deposition step, without the use of ultra-high vacuum chambers by controlling the device fabrication and cleanliness of the chamber.

A challenge to lifetime

The impact of the miniscule amounts of impurities on the lifetime of OLEDs have proved to be a major challenge facing organic devices fabricated by spin-coating, inkjet, and other printing methods, as a result, elimination of impurities get even more difficult.

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