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

Abstract

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.

Molecular dynamic‐secondary ion mass spectrometry (D‐SIMS) ionized by co‐sputtering with C60+ and Ar+

“…Co‐sputtering with a 10 kV C 60 + and a 0.2 kV Ar + beam is known to preserve the chemical structure of the remaining surface for various organic/polymeric materials . Using the co‐sputtering beam as the ionization source, molecular D‐SIMS spectra were also acquired (Fig.…”

“…The apparatus is based on a PHI 5000 VersaProbe (ULVAC‐PHI, Chigasaki, Japan) scanning X‐ray microprobe system operated at a base pressure of <1 × 10 –7 Pa, which was achieved by evacuation using ion getter pumps. The Ar + ion source was operated at 0.2 kV and 300 nA (measured on an Au target) using a floating voltage of 500 V. A voltage setting of 0.2 kV has been previously found to preserve the chemical structure of the remaining surface for various organic/polymeric materials while yielding a more stable sputtering rate . The ray path contained a 1° bend to filter fast Ar atoms.…”

“…Throughout the study of these cluster ion sources, buckminsterfullerene (C 60 + ) has received significant attention since it became a commercially available product in 2003 . Using surface analysis techniques and C 60 + ion sputtering, biological/medical and organic electronic materials have been widely studied.…”

“…This was feasible because the auxiliary Ar + beam could suppress the carbon deposition and/or remove graphitized materials through the removal of the top surface . To date, this co‐sputtering technique has only been used as a slicing tool that removes the outermost surface, while the newly exposed surface is analyzed using other means (namely, X‐ray photoelectron spectrometry and scanning probe microscopy). In previous studies, the sputtered materials were not analyzed, making it unclear how the auxiliary Ar + beam affected the mass distribution of secondary ions and whether the co‐sputtering technique could serve as an ionization source for the dynamic SIMS (D‐SIMS) analysis of organic materials.…”

Back Migration Based Long Lifetime Approach for Organic Light‐Emitting Diode

“…The same SIMS experiments show these atoms to have back‐migrated toward their original electrodes upon a reverse bias at 14 V for 120 min. Our prior study showed that there existed Al spikes protruding into the organic layer . Those Al‐spike facing layer materials would experience a tremendously high electric field and break down electrically at elevated voltages due to their limited dielectric strength.…”