Improved Tandem Organic LEDs

Stacking organic light emitting diodes (OLEDs) leads to brighter, stabler, longer lived light sources than individual OLEDs. Unfortunately, the metal layers typically used to connect the individual elements are not very transparent, reducing the resulting brightness of underlying OLEDs in a tandem configuration.

Researchers in the Display Technology Laboratory at Eastman Kodak Company have now managed to stack OLEDs that are connected through optically transparent, organic semiconductor materials. The improvement in brightness in the new, tandem OLED is essentially linearly related to the number of individual light emitting segments included in the device, that is, a three-segment tandem OLED is roughly three times as bright as a conventional OLED.

High brightness, high efficiency tandem OLEDs could lead to brighter TV's and computer screens. They could also make it easier to read cell phone displays in bright sunlight, which often renders existing cell phone displays unintelligible.

The researchers (contact: L. S. Liao, liang-sheng.liao@kodak.com) propose that tandem OLEDs may also be useful as lighting sources for liquid crystal display backlighting or as solid-state room lights. In addition, varying the number of units in a tandem OLED stack changes the operating voltage, allowing the possibility of tailoring the devices to match different electrical sources, such as household 110 volt systems. Conventional LED lighting, on the other hand, typically requires transformers to adjust power sources to meet the lighting element's electrical specifications. (L. S. Liao et al., Applied Physics Letters, upcoming article)