OLED Emitting Layer Split Between Fluorescence and Yellow Phosphorescence
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Solution Overview
Problem
Current light-emitting elements using organic compounds for electroluminescence face challenges in achieving high emission efficiency, particularly in maintaining luminance and efficiency over time due to the degradation of phosphorescent materials emitting shorter wavelengths.
Innovation Solution
A light-emitting element structure is developed with a first light-emitting layer containing a fluorescent material and a host material, and a second light-emitting layer comprising a phosphorescent material, an organic compound, and another organic compound forming an exciplex, where energy is transferred from the exciplex to the phosphorescent material, optimizing energy levels and carrier balance to enhance emission efficiency and reduce degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent materials are used for emitting shorter wavelengths, then emission efficiency can be improved, but the materials degrade over time reducing luminance and efficiency
Solution Approach 1:
The light-emitting layer is divided into two distinct segments: a first light-emitting layer containing fluorescent material for shorter wavelengths, and a second light-emitting layer containing phosphorescent material for yellow emission. This segmentation allows each material to operate in its optimal wavelength range, preventing the degradation issues associated with using phosphorescent materials for shorter wavelengths while maintaining high emission efficiency.
Solution Approach 2:
Different regions of the light-emitting element are assigned different material compositions optimized for specific functions. The first light-emitting layer uses fluorescent material specifically for blue/green wavelengths where phosphorescent materials would degrade, while the second light-emitting layer uses phosphorescent material specifically for yellow emission where it provides superior efficiency. This local optimization of material properties resolves the contradiction between efficiency and reliability.
2Device complexity
If a single light-emitting layer is used, then device structure is simpler, but emission efficiency and color rendering are insufficient
Solution Approach 1:
The light-emitting element is segmented into two functional layers within the EL layer, each optimized for specific emission characteristics. This segmentation achieves superior emission efficiency and color rendering by utilizing the complementary strengths of fluorescent and phosphorescent materials, while the overall structure remains relatively simple with both layers contained within a single EL layer between the electrodes.
Solution Approach 2:
The light-emitting element employs a composite structure combining fluorescent and phosphorescent materials in distinct layers. This composite approach enables the device to achieve high emission efficiency across multiple wavelengths (blue/green from fluorescent, yellow from phosphorescent) while maintaining a manageable structural complexity. The composite material strategy resolves the contradiction by achieving superior performance through material diversity rather than structural complexity.
3Use of energy by moving object
If phosphorescent material is used for all wavelengths, then emission efficiency is maximized, but degradation occurs particularly at shorter wavelengths
Solution Approach 1:
The emission spectrum is segmented into different wavelength ranges handled by different materials: fluorescent material handles the blue/green region where phosphorescent materials would degrade, while phosphorescent material handles the yellow region where it provides superior efficiency. This segmentation preserves the lifespan of the device by preventing phosphorescent materials from operating in their degradation-prone wavelength range, while maintaining maximum emission efficiency in their optimal range.
Solution Approach 2:
The invention changes the operational parameters of different materials by assigning them specific wavelength ranges. Fluorescent material is parameterized for blue/green emission, phosphorescent material for yellow emission. This parameter optimization ensures each material operates in its most stable and efficient regime, extending device lifespan while maintaining maximum emission efficiency. The parameter change resolves the contradiction by matching material properties to operational conditions.
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 improves emission efficiency, allows for white light emission with high color rendering, and extends the lifespan of the light-emitting element by utilizing fluorescence for shorter wavelengths to minimize degradation, while phosphorescence provides efficient yellow emission.
Implementation Method 1
The first organic compound and the second organic compound form an exciplex
Implementation Method 2
energy is transferred from the exciplex to the phosphorescent material
Implementation Method 3
The second light-emitting layer includes a phosphorescent material
Implementation Method 4
The first light-emitting layer includes a fluorescent material
Data Source
AI summary
Emission efficiency of a light-emitting element is improved. The light-emitting element has a pair of electrodes and an EL layer between the pair of electrodes. The EL layer includes a first light-emitting layer and a second light-emitting layer. The first light-emitting layer includes a fluorescent material and a host material. The second light-emitting layer includes a phosphorescent material, a first organic compound, and a second organic compound. An emission spectrum of the second light-emitting layer has a peak in a yellow wavelength region. The first organic compound and the second organic compound form an exciplex.