Engineers at Osram AG (Munich, Germany) have developed a stacked organic light-emitting diode (OLED) architecture that improves output characteristics and increases lifetime compared to conventional single-active-layer OLEDs. In the stacked-OLED process, undoped and organic active layers—the emissive layer (EML) with red/green/blue (RGB) layers—are first embedded in p-type and n-type doped layers to create a single p-i-n diode or single-active-layer OLED. When three devices are stacked, for example, electron-hole pairs are created at charge-generation layers (CGLs). A twofold white-emitting stacked device achieves the same luminance levels as a single p-i-n device at half the current and twice the voltage.
Because stacked devices have a much higher differential resistivity, stacking improves uniformity of large-area OLEDs without the need to deposit thin metal bus lines on the transparent conductive oxide layer. And because the individual emission values (and corresponding aging mechanisms such as temperature and current density) are lowered for each layer in a stacked device, the overall stacked OLED has a longer lifetime. Contact Christian Boelling at [email protected].
