Organic EL Device Infrared Layer Hole Management
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Solution Overview
Problem
The degradation of color purity in organic EL devices due to the mixing of red, green, and blue light emissions, caused by holes passing through luminescent layers and recombining in the blue luminescent layer, which affects the color developability and luminous efficiency.
Innovation Solution
Incorporating a third luminescent layer emitting infrared light, formed by vapor deposition between the first and second luminescent layers, to consume excess holes and prevent mixing of colors, along with optimized hole injection layers and a cathode structure to enhance luminous efficiency and color purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a blue luminescent layer is formed by vapor deposition over the entire surface including red and green luminescent layers, then the blue luminescent layer achieves sufficient luminous efficiency and emission lifetime for practical use, but holes injected into the red or green luminescent layer may pass through to reach the blue luminescent layer and recombine to emit blue light, causing color purity degradation
Solution Approach 1:
An infrared luminescent layer is introduced as an intermediary between the red/green luminescent layers and the blue luminescent layer. This intermediate layer absorbs holes that would otherwise pass through to the blue luminescent layer, preventing unwanted blue light emission in red and green sub-pixels while maintaining the benefits of vapor-deposited blue luminescent layer
Solution Approach 2:
The infrared luminescent layer is selectively positioned only in regions where red and green luminescent layers are present, allowing different functional characteristics in different regions: hole absorption in red/green sub-pixel regions while permitting hole transport in blue sub-pixel regions
2Ease of manufacture
If liquid application is used to form the blue luminescent layer, then patterning is facilitated and material usage is efficient, but the blue luminescent layer does not achieve sufficient luminous efficiency and emission lifetime for practical use
Solution Approach 1:
The invention combines two different formation methods: liquid application is used for red and green luminescent layers (utilizing its patterning and material efficiency advantages), while vapor deposition is used for the blue luminescent layer (achieving sufficient luminous efficiency and emission lifetime). The infrared luminescent layer is formed by vapor deposition to work synergistically with the blue luminescent layer
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 solution significantly enhances color purity and luminous efficiency by reducing unwanted blue light emission in red and green sub-pixels, allowing for high color developability and long emission lifetime in organic EL devices.
Implementation Method 1
By applying a voltage between the anode and the cathode, holes and electrons are injected respectively from the electron transport layer and the hole transport layer to the luminescent layer and are thus recombined with each other, thereby emitting light
Implementation Method 2
A second luminescent layer is formed by vapor deposition over the entirety of the first and second regions, between the first luminescent layer and the cathode and between the second anode and the cathode
Data Source
AI summary
An organic EL device has a pixel including a red, a green and a blue sub-pixel. The organic EL device includes anodes disposed in the sub-pixels, and a cathode. A red luminescent layer is formed by liquid application between the anode and the cathode, and a green luminescent layer is formed by liquid application between the anode and the cathode. A blue luminescent layer is formed by vapor deposition over the entire region of the red, green and blue sub-pixels between the red and green luminescent layers and the cathode, and between the anode and the cathode in the blue sub-pixel. An infrared luminescent layer is formed by vapor deposition over the entire region of the red, green and blue sub-pixels between the red and green luminescent layers and the blue luminescent layer, and between the anode and the blue luminescent layer in the blue sub-pixel.