Tandem Organic EL Element with Charge Generating Layers
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Solution Overview
Problem
Conventional organic electroluminescent elements fail to provide white light with high color temperature and excellent color rendering properties, limiting their performance as light sources for lighting devices.
Innovation Solution
An organic electroluminescent element with a tandem structure comprising a red phosphorescent light emitting unit, a blue fluorescent light emitting unit, and another blue fluorescent light emitting unit, separated by charge generating layers, which emits white light with a continuous spectrum from 380 nm to 780 nm, achieving balanced peak wavelengths in the red, green, and blue bands for enhanced luminance and color rendering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If three light emitting layers of red, blue, and green are used to provide white light, then color rendering property is improved, but color temperature control and luminance efficiency deteriorate
Solution Approach 1:
The invention divides the white light emission into multiple independent light emitting units (first blue emitting unit, second blue emitting unit, and orange emitting unit) separated by charge generating layers. Each unit emits light at specific wavelengths, and their combined output achieves the desired color temperature and color rendering properties. This segmentation allows independent optimization of each unit's emission characteristics.
Solution Approach 2:
Different light emitting units are assigned different emission characteristics: the blue emitting units provide short wavelength light for high color temperature, while the orange emitting unit provides long wavelength light for color rendering. The charge generating layers are positioned at specific locations to separate and control the emission from each unit, achieving local optimization of emission properties.
2Illumination intensity
If multiple light emitting units are stacked to increase luminance, then luminance efficiency is improved, but device complexity increases
Solution Approach 1:
The invention combines multiple light emitting units with different emission characteristics into a single integrated element structure. The blue emitting units and orange emitting unit are merged through the charge generating layers to produce white light with high luminance. This merging achieves luminance multiplication while maintaining a relatively simple overall structure compared to conventional approaches.
Solution Approach 2:
Charge generating layers are introduced as intermediary components between the light emitting units. These layers facilitate charge transfer and enable the multiple units to operate independently yet cooperatively, achieving high luminance without requiring complex interconnections or control mechanisms between units.
3Ease of manufacture
If conventional organic EL element structure is used, then manufacturing simplicity is maintained, but white light quality for lighting applications deteriorates
Solution Approach 1:
The conventional single-layer structure is segmented into multiple light emitting units (first blue emitting unit, second blue emitting unit, orange emitting unit) separated by charge generating layers. This segmentation enables precise control over the emission spectrum to achieve high color temperature and excellent color rendering properties suitable for lighting applications, while maintaining compatibility with conventional manufacturing processes.
Solution Approach 2:
The invention uses composite light emitting units combining different organic compounds with specific emission characteristics. The blue emitting units use compounds emitting in the 440-490 nm range, while the orange emitting unit uses compounds emitting in the 580-650 nm range. This composite approach achieves superior white light quality while maintaining ease of manufacture through established organic EL fabrication techniques.
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 proposed organic electroluminescent element achieves high luminance and long-life light emission with excellent color rendering properties, suitable for lighting applications, providing white light with a color temperature suitable for daylight, neutral white, and white chromaticity ranges, and an average color rendering index of 70 or more.
Implementation Method 1
An organic EL element is a self-luminous element including a light emitting layer made of an organic compound between a cathode and an anode facing each other. When voltage is applied between the cathode and the anode, electrons injected into the light emitting layer from the cathode side and holes injected into the light emitting layer from the anode side recombine in the light emitting layer to generate excitons and light is emitted by this excitons.
Implementation Method 2
In this organic EL element with the MPE structure, when voltage is applied between the cathode and the anode, charges in a charge transfer complex move toward each of the cathode side and the anode side and this causes holes to be injected into one light emitting unit located on the cathode side of the charge generating layer and causes electrons to be injected into another light emitting unit located on the anode side of the charge generating layer.
Implementation Method 3
An organic electroluminescent element with a tandem structure comprising a red phosphorescent light emitting unit, a blue fluorescent light emitting unit, and another blue fluorescent light emitting unit
Implementation Method 4
An organic electroluminescent element with a tandem structure comprising a red phosphorescent light emitting unit, a blue fluorescent light emitting unit, and another blue fluorescent light emitting unit
Data Source
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AI summary
This organic EL element (10) comprises a first light emitting unit (21) that contains a red phosphorescent light emitting layer and a green phosphorescent light emitting layer, a second light emitting unit (22) that contains a blue fluorescent light emitting layer, and a third light emitting unit (23) that contains a blue fluorescent light emitting layer; and this organic EL element (10) has a structure in which a positive electrode (12), the third light emitting unit (23), a second charge generating layer (32), the second light emitting unit (22), a first charge generating layer (31), the first light emitting unit (21) and a negative electrode (11) are sequentially laminated in this order. The white light obtained through light emission of the first light emitting unit (21), the second light emitting unit (22) and the third light emitting unit (23) has one peak wavelength within the red wavelength range of from 590 nm to 640 nm, one peak wavelength within the green wavelength range of from 500 nm to 550 nm, and one or two peak wavelengths within the blue wavelength range of from 440 nm to 490 nm.