White OLEDs - the next generation light source

The Technical University of Dresden and Novaled AG have reached 90 lm/W at a brightness of 1.000 cd/m2 for a real lighting device and even 124 lm/W when using a 3D light extraction system.

 

White organic light-emitting diodes (OLEDs) are a promising new technology to become the next generation light source. They have the potential of much higher efficiencies than classical lighting sources. Due to their unique features and attractive appearance, white OLEDs will have a striking impact on the lighting industry.

 

These ultra-thin large-area-emitting devices can be flexible, transparent, color-tunable and scaled to virtually any size or shape enabling completely new ways for lighting designers. They have been mainly used in industrialized high-end display applications in displays for MP3 players, mobile phones and the youngest generation of TVs.

 

The key for lighting is power efficiency - Lighting applications count for a quarter of energy spending in Europe. Switching to a more efficient technology like OLEDs may give a 50% saving in electricity bills.

 

For power efficiency, fluorescent tubes are a benchmark for emerging technologies with some 50-70 lm/W (considering losses in reflectors) - The researchers were able to surpass this benchmark by achieving at the very high brightness of 5,000 cd/m2 a power efficiency of 74 lm/W.

 

Researchers at Changchun Institute of Applied Chemistry at the Chinese Academy of Sciences (Beijing) built LEDs from organic, carbon-based materials, like plastic, rather than from more expensive semiconducting materials such as gallium, which also requires more complicated manufacturing processes. They claimed that they demonstrated, for the first time, an organic white-light LED operating within only a single active layer, rather than several sophisticated layers. Moreover, by putting two of these single-layer LEDs together in a tandem unit, higher efficiency was achieved. The scientists reported that their LED was able to achieve a CRI rating of nearly 70 - almost good enough to read by.

 

Philips recently stepped up its investment for OLEDs by establishing a dedicated Business Center in Aachen, Germany, which they claim to be the world's first-ever production line for OLED lighting. The products, which will be marketed under the name of Lumiblade, will include OLED lighting plates of up to 50cm² in a wide range of colors and shapes but the company still needs to address many challenges such as higher brightness levels, longer lifetimes and good quality of white and mixed colors.

 

We are unlikely to see mass produced OLEDs until all technological barriers are removed. White OLEDs degrade within an hour or two, because the polymers that produce the blue part of the light are unstable but promising first results on stable, phosphorescent blue polymers are starting to emerge although it may take a few years. Even a tiny dust particle can destroy an OLED before it is produced, making fabrication of larger panels expensive and complicated.

 

Currently OLEDs do not maintain brightness long enough to compete with traditional light sources. They need to be significantly improved so that higher efficiency, lower production costs and longer lifetime are achieved.

 

To learn more attend Printed Electronics Asia 2009  or Printed Electronics USA 2009 .

 

Also read OLED100.eu research consortium to spearhead the advancement of OLEDs, A major milestone - white OLED technology exceeds 100 lm/W and International standard for white color OLED requirements met.