Inverted OLED Buffer Layer for Voltage and Lifetime Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Inverted-structure light-emitting elements with alkali metal or alkaline earth metals in the electron-injection layer experience increased driving voltage and reduced lifetime due to contact with oxide semiconductor cathodes, particularly when an oxide conductive film is used.
Innovation Solution
Incorporating a buffer layer with an electron-transport material, such as bathophenanthroline, between the cathode and the electron-injection layer to prevent diffusion of alkali or alkaline earth metals and facilitate carrier injection, thereby reducing driving voltage and improving efficiency and longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an electron-injection layer containing alkali metal or alkaline earth metal is stacked directly over the cathode in an inverted-structure light-emitting element, then the element structure is simplified and manufacturing is easier, but the driving voltage increases and the lifetime is shortened
Solution Approach 1:
An electron-transport layer is introduced as an intermediary between the cathode and the electron-injection layer. This intermediate layer prevents direct contact between the oxide semiconductor cathode and alkali/alkaline earth metals in the electron-injection layer, thereby eliminating the harmful diffusion while maintaining the inverted structure's manufacturing advantages. The electron-transport layer serves as a protective barrier that preserves element lifetime without complicating the manufacturing process.
2Device complexity
If an electron-injection layer containing alkali metal or alkaline earth metal is stacked directly over the cathode, then the structure is simpler, but the driving voltage increases
Solution Approach 1:
The electron-transport layer acts as a mediator that resolves the conflict between structural simplicity and driving voltage reduction. By placing this intermediate layer between the cathode and electron-injection layer, the structure remains relatively simple while the driving voltage is reduced because the intermediate layer prevents harmful interactions that would otherwise increase voltage requirements.
Solution Approach 2:
The invention uses a composite layered structure combining the cathode, electron-transport layer, and electron-injection layer. This composite approach allows each layer to perform its specific function: the cathode provides electron injection, the electron-transport layer prevents metal diffusion and facilitates carrier transport, and the electron-injection layer supplies electrons to the light-emitting layer, achieving low driving voltage without excessive structural complexity.
3Ease of manufacture
If alkali metal or alkaline earth metal in the electron-injection layer contacts the oxide semiconductor cathode, then the manufacturing process is simpler, but power efficiency decreases
Solution Approach 1:
The electron-transport layer serves as a protective intermediary that prevents direct contact between the oxide semiconductor cathode and alkali/alkaline earth metals. This intermediate barrier eliminates the harmful diffusion that would otherwise occur, thereby maintaining high power efficiency while keeping the manufacturing process simple and straightforward.
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
The buffer layer effectively suppresses metal diffusion, lowering the driving voltage, enhancing power efficiency, and extending the lifespan of the light-emitting element by ensuring proper carrier injection and maintaining optimal electron transport properties.
Implementation Method 1
a first layer between the cathode and the light-emitting layer, and a second layer between the first layer and the light-emitting layer. The second layer includes an alkali metal or an alkaline earth metal. The first layer includes an electron-transport material.
Data Source
AI summary
An inverted-structure light-emitting element is provided. One embodiment of the invention disclosed in this specification is a light-emitting element including a cathode, a layer serving as a buffer over the cathode, an electron-injection layer over the layer serving as a buffer, a light-emitting layer over the electron-injection layer, and an anode over the light-emitting layer. The electron-injection layer includes an alkali metal or an alkaline earth metal. The layer serving as a buffer includes an electron-transport material. In the inverted-structure light-emitting element, contact of the alkali metal or alkaline earth metal included in a material of the electron-injection layer with the already formed cathode increases the driving voltage of an EL element and reduces emission efficiency. This problem becomes prominent particularly when the cathode includes an oxide conductive film. To prevent this, the layer serving as a buffer is provided between the cathode and the electron-injection layer.