White OLED HOMO Level Inversion for Chromaticity Stability
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Solution Overview
Problem
White organic electroluminescent elements face challenges in maintaining chromaticity stability due to the sensitivity of dopant ratios, leading to deviations in color emission and production instability.
Innovation Solution
An organic electroluminescent element with a light emitting layer containing three types of materials emitting blue, green, and red light, where the material with the shortest wavelength has a lower HOMO level, allowing for a larger proportion of longer wavelength materials and reducing the sensitivity of dopant ratios, is used. The light emitting layer includes a phosphorescent compound and is produced using a coating process with a thickness of at least 15 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If RGB emitting materials are incorporated in a single emitting layer with conventional HOMO level arrangement, then white light emission is achieved, but chromaticity deviation occurs due to sensitivity of dopant ratios
Solution Approach 1:
The patent changes the HOMO level parameter arrangement among the emitting materials. Specifically, it arranges the HOMO levels such that the shortest wavelength material has the highest HOMO level, intermediate wavelength material has intermediate HOMO level, and longest wavelength material has the lowest HOMO level. This parameter change in energy level arrangement resolves the chromaticity instability issue while maintaining white light emission.
Solution Approach 2:
The patent uses a composite light emitting layer containing three types of emitting materials (blue, green, and red dopants) with specifically arranged HOMO levels. This composite structure allows energy transfer from higher HOMO level materials to lower HOMO level materials, achieving stable white light emission with reduced sensitivity to dopant ratio variations.
2Quantity of substance
If energy transfer is considered in single layer RGB emitting materials, then longer wavelength materials require less dopant, but production stability becomes insufficient
Solution Approach 1:
The patent changes the HOMO level parameter arrangement to optimize dopant quantity distribution. By setting the shortest wavelength material with highest HOMO level and longest wavelength material with lowest HOMO level, the patent achieves energy transfer cascade that reduces overall dopant sensitivity while maintaining appropriate dopant amounts for each color component.
3Ease of operation
If HOMO level of longer wavelength material is smaller, then carrier trapping occurs by longer wavelength guest material, but chromaticity deviation occurs
Solution Approach 1:
The patent inverts the conventional HOMO level arrangement. Instead of longer wavelength materials having smaller HOMO levels, the patent arranges them with progressively lower HOMO levels from shortest to longest wavelength. This creates a downward energy cascade that improves carrier trapping efficiency while stabilizing chromaticity through controlled energy transfer.
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 approach stabilizes the chromaticity and production stability of white light emission by reducing the variation in dopant ratios and allowing for a higher proportion of longer wavelength materials, resulting in a consistent and efficient white organic electroluminescent element.
Implementation Method 1
The organic EL element emits light in such way that high electric field is acted to emitting part, and electrons are accelerated in the high electric field to come into collision to emission center whereby the emission center is activated to make light emission
Implementation Method 2
the light emitting layer contains at least three types of light emitting materials different from each other in λ max, and an absolute value of HOMO level of the light emitting material having the shortest wavelength is smaller than the absolute value of HOMO level of the other light emitting materials
Data Source
AI summary
The present invention provides a white organic electroluminescent element which can emits white light and is free from deviation of chromaticity. This organic electroluminescent element comprises a substrate and, provided on the substrate, at least an anode, a cathode, and a light emitting layer held between the anode and the cathode. This organic electroluminescent element is characterized in that the light emitting layer contains at least three types of light emitting materials different from each other in λ max, and the absolute value of HOMO level of the light emitting material having the shortest wavelength is smaller than the absolute value of HOMO level of the other light emitting materials.