Pure white organic light-emitting diode with lifetime approaching the longevity of yellow emitter.

A high-efficiency pure white organic light-emitting diode was fabricated with lifetime approaching that of the low-excitation-energy (yellow) emitter containing counterpart, or six times that of the deep-blue counterpart. The white device was composed of two emission layers with mixed hosts of different compositions. They were respectively doped with yellow rubrene and deep-blue 4,4'-bis-[4-{N,N,N',N'- tetrakis-(4-fluoro-diphenylamino)-phenyl}-vinyl]-biphenyl. The resulting efficiency was 6.0 lm/W (12.4 cd/A) at 20 mA/cm(2). The long device lifetime may be attributed to the double mixed-host architecture employed that effectively dispersed the injected carriers into three different recombination zones and consequently diluted the damaging effect arising from the accumulated charge from un-recombined carriers, hence leading to a markedly improved lifespan.

Extraordinarily high efficiency improvement for OLEDs with high surface-charge polymeric nanodots.

The efficiency of highly efficient blue, green, red, and white organic light-emitting diodes (OLEDs) has been substantially advanced through the use of high surface-charge nanodots embedded in a nonemissive layer. For example, the blue OLED's markedly high initial power efficiency of 18.0 lm W(-1) at 100 cd m(-2) was doubled to 35.8 lm W(-1) when an amino-functionalized polymeric nanodot was employed. At high luminance, such as 1000 cd m(-2) used for illumination applications, the efficiency was improved from 12.4 to 21.2 lm W(-1), showing a significant enhancement of 71%. The incorporated highly charged nanodots are capable of effectively modulating the transportation of holes via a blocking or trapping mechanism, preventing excessive holes from entering the emissive layer and the resulting carrier-injection imbalance. Furthermore, in the presence of a high-repelling or dragging field arising from the highly charged nanodots, only those holes with sufficient energy are able to overcome the included barriers, causing them to penetrate deeper into the emissive layer. This penetration leads to carrier recombination over a wider region and results in a brighter emission and, therefore, higher efficiency.