Alkali Metal Oxide Electron Injection Layer for OLEDs
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Solution Overview
Problem
In organic electroluminescence devices, achieving balanced electron and hole injection while minimizing operating voltage is challenging, as low work function metals are reactive and halogen elements in existing cathode structures can quench light emission.
Innovation Solution
An electron injection layer with a material represented by formula AxByOz, where A is an alkali or alkali earth metal and B is a group VIII metal, is introduced between the cathode and organic layer, with preferred materials like LiNiO2 or LiCoO2, and a thickness of 0.5-20 nm to enhance electron injection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a low work function metal is used as cathode to improve electron injection ability, then electron injection efficiency is improved, but the metal is too active and reacts with water and oxygen causing device instability
Solution Approach 1:
An electron injection layer composed of alkali metal oxide or hydroxide (such as Li2O, LiOH, Na2O, NaOH) is introduced as an intermediary between the cathode and the organic layer. This intermediary layer provides excellent electron injection capability while being chemically stable and resistant to reactions with water and oxygen, thus resolving the contradiction between injection efficiency and device stability.
Solution Approach 2:
The invention changes the material parameters by using compounds with specific properties (alkali metal oxides and hydroxides) that have both high electron injection capability and chemical stability. By controlling the thickness of this layer (0.1-10 nm), the invention optimizes the balance between injection efficiency and stability, avoiding the reactivity issues of pure low work function metals.
2Productivity
If LiF/Al cathode structure is used to improve electron injection ability, then electron injection efficiency is improved, but halogen elements cause quench of light emission
Solution Approach 1:
The invention extracts and removes the harmful halogen elements (fluorine in LiF) from the cathode structure while retaining the beneficial electron injection capability. By replacing LiF with alkali metal oxides or hydroxides that do not contain halogens, the invention eliminates light quenching while maintaining excellent electron injection performance.
Solution Approach 2:
The invention converts the search for high electron injection capability (which led to harmful halogen-containing materials) into a beneficial approach by using alkali metal oxides and hydroxides. These materials naturally provide high electron injection efficiency without the harmful side effects of halogen-induced light quenching, thus turning the requirement for high injection into a pathway for achieving both efficiency and optical compatibility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration results in high electron injection efficiency, low operating voltage, high luminance, and extended device life, outperforming traditional LiF/Al structures in OLEDs.
Implementation Method 1
improve electron injection ability
Implementation Method 2
high efficiency of injecting electrons from a cathode to an organic layer
Data Source
AI summary
The present invention relates to an organic electroluminescence device and provides a new material composition scheme for an electron injection layer. The organic electroluminescence device of the present invention includes an electron injection layer which contains a material represented by formula AxByOz, wherein A is one of an alkali metal and an alkali earth metal, B is one of group VIII metals and 0<x≦2, 0<y≦3, 0<z≦6. A is selected from one of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr and Ba. B is selected from one of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt. The electron injection layer can be formed of Al and AxByOz. The electron injection layer has high electron injection ability, and the device has low threshold voltage, high luminance, high efficiency and long life.