Organic EL Device Layer Inversion for Balanced Emission
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Solution Overview
Problem
Current organic EL devices with a configuration of blue, green, and red light emitting layers laminated from the hole transport layer side suffer from varying emission spectra, insufficient luminous efficacy, and imbalance in luminous intensities, making them unsuitable for full-color display applications comparable to CRTs.
Innovation Solution
An organic EL device configuration with a red light emitting layer, a green light emitting layer, and a blue light emitting layer laminated in that order from the anode side, where the red layer has hole transporting properties, the green layer has positive and negative charge transporting properties, and the blue layer has electron transporting properties, allowing controlled injection of holes and electrons for enhanced emission efficacy and longer luminance half-life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a blue light emitting layer, a green light emitting layer, and a red light emitting layer are laminated in this order from the hole transport layer side, then the device can emit white light with three wavelength components, but the emission spectrum varies largely with current and the luminous efficacy and half life of luminance are insufficient
Solution Approach 1:
The patent inverts the conventional lamination order of light emitting layers. Instead of blue-green-red from the hole transport layer side, it uses red-green-blue from the hole transport layer side (or equivalently, blue-green-red from the anode side). This inversion optimizes hole and electron injection balance, stabilizes the emission spectrum across different current levels, and improves both luminous efficacy and half life of luminance.
2Device complexity
If the conventional lamination order (blue, green, red from hole transport layer side) is used, then the device structure is simple, but the balance of respective luminous intensities in blue, green and red wavelength regions is insufficient
Solution Approach 1:
The patent assigns different charge transporting properties to different light emitting layers to optimize local charge injection. The red light emitting layer has hole transporting property, the green light emitting layer has positive and negative charge transporting properties, and the blue light emitting layer has electron transporting property. This local differentiation of transport characteristics achieves balanced luminous intensities across all three color regions.
3Productivity
If the red light emitting layer has hole transporting property, then holes injected from the anode are efficiently supplied to the light emitting layers, but the device complexity increases
Solution Approach 1:
The red light emitting layer material serves multiple functions simultaneously: it emits red light and also transports holes. By selecting a red light emitting material with inherent hole transporting capability, the patent eliminates the need for a separate hole transport layer, thereby improving hole injection efficiency without significantly increasing device complexity.
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 achieves stable, balanced emission of red, green, and blue light components with high efficiency and color purity, enabling a display with improved color reproduction performance and extended operational life.
Implementation Method 1
an organic EL device in which an organic layer including a plurality of light emitting layers is interposed between an anode and a cathode
Data Source
AI summary
An organic EL device and display are provided. An organic EL device which has light emission components in three colors of red, green and blue in a good balance suited to use for a full-color display and which is capable of highly efficient and stable light emission for a long time. In the organic EL device including an organic layer having light emitting layers sandwiched between an anode and a cathode, the light emitting layers include a red light emitting layer, a green light emitting layer, and a blue light emitting layer laminated in this order from the side of the anode. The red light emitting layer contains a hole transporting light emitting material and has a hole transporting property. In addition, the green light emitting layer has a positive and negative charge transporting property. Furthermore, the blue light emitting layer has an electron transporting property, and includes a positive and negative charge transporting blue light emitting layer and an electron transporting blue light emitting layer laminated in this order from the side of the anode.