OLED with non-constant dopant concentration profiles have been processed by means of organic vapour phase deposition (OVPD) and were compared with regard to their luminous current efficiencies. Especially when driven at ultra-high luminance (>10,000 cd/A), OLED with a dopant concentration profile starting with a rather high dopant concentration on the anode side of the emissive layer showed improved luminous current efficiencies compared to their conventional counterparts.

To further investigate this effect, the width and location of the recombination zone have been simulated for all investigated concentration profiles by numerical solution of the semiconductor device equations using experimentally determined doping-dependent charge carrier mobilities. The obtained theoretical results are discussed with regard to the accomplished experiments.

The current and luminous efficacy of a red phosphorescent organic light emitting diode (OLED) with sharp interfaces between each of the organic layers can be increased from 18.8 cd/A and 14.1 lm/W (at 1,000 cd/m2) to 36.5 cd/A (+94%, 18% EQE) and 33.7 lm/W (+139%) by the introduction of a layer cross-fading zone at the hole transport layer (HTL) to emission layer (EL) interface. Layer cross-fading describes a procedure of linearly decreasing the fraction in growth rate of an organic layer during deposition over a certain thickness while simultaneously increasing the fraction in growth rate of the following layer. For OLED processing and layer cross-fading organic vapor phase deposition (OVPD) is used. The typical observation of a roll-off in current efficacy of phosphorescent OLED to higher luminance can be reduced significantly. An interpenetrating network of a prevailing hole and a prevailing electron conducting material is created in the cross-fading zone. This broadens the recombination zone and furthermore lowers the driving voltage. The concept of layer cross-fading to increase the efficacies is suggested to be useful in multi-colored OLED stacks as well.

Organic light-emitting diodes (OLED) offer the potential to replace conventional light sources such as incandescent bulbs and fluorescent tubes. The question which thin-film technology is most favorable to produce OLED on an industrial scale is still unanswered. The most established technology for the deposition of small-molecule organic layers is vacuum thermal evaporation. A comparably novel technology is organic vapor phase deposition (OVPD), which offers some unique features in terms of adjustable process parameters such as deposition chamber pressure (P) and substrate temperature (TS). The impact of these parameters on the morphology of organic single layers as well as on the performance of OLED is mostly unknown. In this work, phosphorescent red OLED were produced with different TS and a strong influence on the device efficiency was found. Atomic force microscopy measurements were conducted to investigate the morphology of the hole injection and hole transport layers of the devices deposited at different TS. In addition to this, the influence of TS and P on the performance of fluorescent blue OLED and the morphology of organic single layers was tested. By varying TS and P for the emission layer only, current efficiencies in the range from 4.3 to 6.8 cd/A were found despite the fact that all devices had the same structure. Atomic force microscopy measurements conducted on organic single layers which were deposited at the same process conditions showed rms values ranging from 1.4 to 57 nm.

In this work, organic light emitting devices (OLEDs) based on a blue-emitting fluorescent guest/host-system from Merck OLED Materials GmbH is investigated. OLEDs comprising a hole transport layer (HTL), the emissive film Merck Blue Host:Merck Blue Guest (MBH:MBG), a hole-blocking film and the electron transport layer (ETL) were prepared by vacuum thermal evaporation. The hole-blocking capabilities of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq) and the host material MBH were investigated. By employing an additional HBL, the current efficiency could be increased from 5.7 to 7.4 cd/A. Furthermore, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) doping of the HTL was investigated. Devices with 4,7-diphenyl-1,10-phenanthroline (BPhen) or 1,3,5-Tris-(N-phenylbenzimidazol-2-yl)benzene (TPBI) as alternative ETLs were fabricated and conclusions were drawn regarding the charge balance in the devices. It was found that employing tris-(8-hydroxyquinoline) aluminum (Alq3) as ETL leads to the best lifetimes of about 2000 hours at a constant current of 20 mA/cm2 while p-doping in combination with BPhen as ETL leads to the highest efficiency of 5.7 lm/W max. and 4.4 lm/W at 1000 cd/m2.