With OLEDs approaching production maturity, Osram has announced that it is researching another technology that could change the world of lighting: light emitting foils produced in a printing process. The foils are based on light-emitting electrochemical cells made from organic materials, known as organic light-emitting electrochemical cells (OLECs). Although similar to OLEDs, they have a conductive and light-emitting layer containing a liquid material instead of a solid material. This active layer contains freely mobile ions in the liquid phase. When a voltage is applied to the active layer, the ions migrate to the edge. This allows charge carriers to be injected into the layer, where they recombine to emit light in the same way as a light-emitting diode. With suitable combinations of materials, any desired color of light can be obtained.
The first OLEC modules have been fabricated by first coating a plastic film substrate with a transparent conductive layer. On top of this another conductive polymer layer is applied using a precision slotted nozzle. After an infrared drying step, a light-emitting layer is applied in the same way. Finally, standard metal electrodes are fabricated using vapor deposition. Unlike LED and OLED production, this process does not require cleanroom conditions. The first OLECs produced using this process have an efficiency of 17 lumens per watt in the green region of the visible spectrum, compared with an efficiency of around 10 lm/W with an incandescent lamp.