Effect of Fabrication Parameters on Three-Dimensional Nanostructures and Device Efficiency of Polymer Light-Emitting Diodes

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] (Flrpic) 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 Flrpic 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.