Tuesday, September 30, 2014

University of Michigan showcases 10x increase in the lifetime of blue phosphorescent OLED

 As reported by University of Michigan "Live long and phosphor: Blue LED breakthrough for efficient electronics" In a step that could lead to longer battery life in smartphones and lower power consumption for large-screen televisions, researchers at the University of Michigan have extended the lifetime of blue organic light emitting diodes by a factor of 10.

Blue OLEDs are one of a trio of colors used in OLED displays such as smartphone screens and high-end TVs. The improvement means that the efficiencies of blue OLEDs in these devices could jump from about 5 percent to 20 percent or better in the near future.
The blue PHOLED consisted of a thin film of light-emitting material sandwiched between two conductive layers—one for electrons and one for holes, the positively charged spaces that represent the absence of an electron. Light is produced when electrons and holes meet on the light-emitting molecules. (Picture from University of Michigan FLICKR)
Tenfold increase in the lifetime of blue phosphorescent organic light-emitting diodes

Yifan Zhang, Jaesang Lee & Stephen R. Forrest    
Nature Communications 5, 5008, 25 September 2014, doi:10.1038/ncomms6008 
Organic light-emitting diodes are a major driving force of the current information display revolution due to their low power consumption and potentially long operational lifetime. Although electrophosphorescent organic emitters have significantly lower power consumption than fluorescent emitters, the short lifetime of electrophosphorescent blue devices has prevented their application in displays for more than a decade. Here, we demonstrate a novel blue electrophosphorescent device with a graded dopant concentration profile in a broadened emissive layer, leading to a lower exciton density compared with a conventional device. Thus, triplet-polaron annihilation that leads to long-term luminescent degradation is suppressed, resulting in a more than threefold lifetime improvement. When this strategy is applied to a two-unit stacked device, we demonstrate a lifetime of 616±10 h (time to 80% of the 1,000 cd m−2 initial luminance) with chromaticity coordinates of [0.15, 0.29], representing a tenfold lifetime improvement over a conventional blue electrophosphorescent device.

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