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Abstract
Electron injection in OLED organic layers is improved by usingalkaline-earth or 代写留学生论文alkali metals as cathode layers or as dopantsinside organic layers. An innovative metal dispensing technologyhas been developed to overcome handling problems and to ensurecontrolled and reliable metal layers deposition for OLEDs.

1. Introduction
One of the key issues for organic light emitting diodes (OLEDs) isto achieve high electro-luminescence external quantum efficiency(ηext), high power efficiency (ηE) and long-term stability. Thesegoals imply extremely efficient electron injection and thereforelow driving voltage, together with high electron mobility in theorganic layer and thus high recombination efficiencies. Thecathode structure and the metal-organic interface are the majorresponsible for the desired performance improvements. Bothalkali metals, like Li and Cs, and alkaline-earth metals, like Mgand Ba, are currently used inside OLED architectures to reach theabove purposes.

In case of small molecule OLEDs, alkali metals incorporationinside the device structure can be accomplished in two forms: 1)ultra-thin layers above the electron transport layer (ETL) andcapped by an Al back electrode[2,3]; 2) co-deposition of Li or Cswith an ETL immediately prior to the cathode deposition (alsonamed “alkali metal doping of ETL”).

In case of Top Emission OLED devices, the most promisingtransparent cathode layers can be obtained in two ways: 1) by co-deposition of a Mg:Ag layer above the ETL[7]; 2) by co-depositionof Li or Cs with ETL just before the deposition of ITO ascathode[2,7]. Mg or Mg composite cathodes (using the co-deposition of Ag for instance) are the most widely cathodestructures used for many OLED devices. Basically, Magnesiumalloyed with Silver forms an efficient electron injecting contact onorganic semiconductors: Magnesium is chosen for its low workfunction (3,7 eV) while Ag adds chemical stability to Mg layersand is also believed to increase the sticking coefficient of Mgduring the deposition procedure. Mg is also found to partiallydiffuse into the organic layer (such as Alq3) leading to a broad“doped” interface made by organometallic complexes with astrong dipolar behaviour.

In case of PLED devices, one of the most applied cathode layer ismade of pure Ba.
Saes Getters S.p.A. conducted deep studies to develop solutionsassuming stable and reliable evaporation of Li, Cs, Mg and Ba.The present work specifically discusses Lithium and Magnesiumsources for a controlled evaporation of said metals.

2. Sources and metal evaporation
The deposition of alkali (and alkaline earth) metal layers can beperformed through the metal itself in a conventional heated crucible. However these metals are very reactive and should behandled in inert atmosphere throughout the entire process. This isdifficult to be achieved since even low traces of humidity,Nitrogen and Oxygen, cause their appreciable degradation. Forexample, free metallic Lithium easily reacts with moistureforming LiOH and H2; it also forms Li3N and Li2O when heatedin presence of Nitrogen and Oxygen. Furthermore LithiumHydroxide readily absorbs CO2and water from air. The abovecited reactions can occur whenever the evaporation chamber isopened and also during any evaporation cycles leading to severalinstabilities like splash evaporation, due to reaction at solid-liquidinter本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。