RESUMEN
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.
RESUMEN
By using 10 kV C(60)(+) and 200 V Ar(+) ion co-sputtering, a crater was created on the light-emitting layer of phosphorescent polymer light-emitting diodes, which consisted of a poly(9-vinyl carbazole) (PVK) host doped with a 24 wt % iridium(III)bis[(4,6-difluorophenyl)pyridinato-N,C(2)] (FIrpic) guest. A force modulation microscope (FMM) was used to analyze the nanostructure at the flat slope near the edge of the crater. The three-dimensional distribution of PVK and FIrpic was determined based on the difference in their mechanical properties from FMM. It was found that significant phase separation occurred when the luminance layer was spin coated at 30 degrees C, and the phase-separated nanostructure provides a route for electron transportation using the guest-enriched phase. This does not generate excitons on the host, which would produce photons less effectively. On the other hand, a more homogeneous distribution of molecules was observed when the layer was spin coated at 60 degrees C. As a result, a 30% enhancement in device performance was observed.
