Search

The intermediate blocking layer (IBL) was investigated for the development of highly efficient and bright organic light-emitting diodes (OLEDs). The insertion of an IBL between a hole transport layer and an emitting layer (EML) has resulted in the development of highly efficient and bright OLEDs. The quantum efficiency and electrical durability at high voltage were highly dependent on the thickness of the IBL. The maximum external quantum efficiency of the devices with a 1.5-nm-thick IBL was increased by 28% compared with the reference. The enhanced performance of the OLEDs appears to be due to the improvement of carrier balance and exciton confinement.

Most of organic devices showed poor thermal stability and short lifetime due to Joule heating by current injection during operation. To increase the lifetime of the devices, thermal management must be considered. We demonstrated the polymer light-emitting diodes with thermally conductive substrate and Al/Cu double cathode to enhance the thermal stability of the device. Also, we proposed the correlation between lifetime (Δt) and device heat sink (ΔT). The heat sink of all organic devices is required to enhance device durability.

A semitransparent cathode of indium tin oxide (ITO)/Ag/ITO was developed as a resonant tunneling double barrier structure for transparent organic light-emitting diodes. A weak negative differential resistance was observed in devices using a 100nm thick ITO/Ag/ITO layer as a cathode in combination with a thin LiF∕Al layer. The current injection of devices was dominated by resonant tunneling, which induced no luminance at low voltage. This was achieved by employing an e-beam evaporated ITO/Ag/ITO cathode due to the double quantum barriers of ITO and the quantum well of Ag. The authors also applied the multilayer cathode to small molecule devices, which showed the same resonant tunneling currents.

The authors have investigated the effects of indium tin oxide (ITO) deposited by ion beam assisted e-beam evaporation on the performance of polymer light-emitting diodes. ITO was evaporated as a cathode onto a thin Mg:Ag layer by an e-beam process, and its performance as a transparent cathode was subsequently compared to that of Mg:Ag and sputtering-prepared ITO. Polymer devices’ luminance and efficiency were improved by more than ten times by ion beam assisted deposition (IBAD)-prepared ITO deposition, with little observable damage to the organic layer. Implementation of the IBAD process resulted in the reduction of the interfacial energy barrier which induced band bending. Furthermore, outcoupling with ITO resulted in enhanced luminance.

We investigated the effect of anode rotation on the nucleation and growth of B–C–N nanotubes by the plasma rotating electrode process (PREP). With rotation of the anode and/or increase in metal concentration, the number and length of nanotubes were increased, that is, the yield of B–C–N nanotubes was increased. This result is related to the improvement of discharge characteristics by rotating the anode and/or the enhanced catalytic effect of metal species.

An ultrathin lithium fluoride (LiF) hole injection layer was deposited on an indium-tin-oxide (ITO) anode by an ion-beam-assisted deposition (IBAD) technique to fabricate an organic electroluminescence device. The device with the LiF layer deposited by this method has higher external quantum efficiency than a device with a LiF deposited by conventional thermal evaporation. Moreover, the hole-injection ability of the device prepared by IBAD is better than that of the device produced by a conventional method such as thermal evaporation. It is found that the surface of the LiF layer prepared by IBAD has high surface coverage on an ITO anode because the LiF layer prepared has high adatom mobility due to the ion beam energy.

We report a fabrication of organic light-emitting diodes (OLEDs) based on soluble phenyl-substituted poly-p-phenylene-vinylene (Ph-PPVs) thin films with aluminum cathode prepared by ion-beam-assisted deposition (IBAD). The electrical properties of the aluminum cathode, prepared by IBAD, on Ph-PPV have been investigated and compared to those by thermal evaporation. Energetic particles of Al assisted by an Ar+ ion may damage the organic material generating undesirable leakage current even though a thin Al buffer layer is applied to avoid Ar+-ion-induced damages. Substantial improvements of passivation characteristics were observed in IBAD device because the dense Al cathode inhibits the permeation of H2O and O2 into Ph-PPV film through pinhole defects, and thus retards dark spot growth. These results may be deduced from the highly packed structure that has small contact resistance between Al and Ph-PPV in ion-beam-assisted aluminum devices.