OLED Electron Blocking Layer Segmentation for Voltage Reduction
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Solution Overview
Problem
Existing organic electroluminescent devices with thermally activated delayed fluorescence (TADF) materials face high driving voltage issues due to deep highest occupied molecular orbital (HOMO) energy levels, leading to short service life and high energy consumption.
Innovation Solution
The organic electroluminescent device incorporates a unique structure with multiple electron blocking layers and light-emitting units, including a red, green, and blue light-emitting system, where the blue light electron blocking layer is positioned closer to the light-emitting layer, creating an energy level step that facilitates efficient hole injection and reduces driving voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If TADF materials with deep HOMO energy levels are used in organic electroluminescent devices, then high luminous efficiency is achieved through utilization of both singlet and triplet excitons, but driving voltage becomes excessively high
Solution Approach 1:
The electron blocking layer is segmented into multiple layers with different HOMO energy levels, arranged in a stepped configuration. This segmentation allows progressive energy level matching between the anode and light-emitting layer, reducing the overall driving voltage while maintaining efficient hole injection and electron blocking functions.
Solution Approach 2:
Different regions of the electron blocking layer structure are assigned different HOMO energy levels to perform specialized functions: higher HOMO levels in certain layers for effective electron blocking, and progressively lower HOMO levels in other layers for optimized hole transport and voltage reduction. This local differentiation resolves the contradiction between voltage reduction and functional performance.
2Loss of energy
If TADF materials with deep HOMO energy levels are used, then high luminous efficiency is achieved, but service life is shortened due to high driving voltage
Solution Approach 1:
The electron blocking layer is divided into multiple stepped layers with progressively varying HOMO energy levels. This segmentation creates a gradual energy transition pathway that reduces the overall driving voltage, thereby decreasing electrical stress on device components and extending service life while preserving the high luminous efficiency enabled by TADF materials.
Solution Approach 2:
The HOMO energy level parameter is systematically varied across different layers of the electron blocking structure. By creating a stepped gradient of HOMO levels rather than using a uniform value, the device achieves lower operating voltage and reduced electrical stress, which directly extends service life while maintaining the high efficiency benefits of TADF materials.
3Loss of energy
If TADF materials with deep HOMO energy levels are used, then high luminous efficiency is achieved, but energy consumption increases due to high driving voltage
Solution Approach 1:
The electron blocking layer is segmented into multiple layers with stepped HOMO energy levels, creating an energy cascade that facilitates efficient charge transport at lower voltage. This segmentation reduces the overall energy input required to drive the device while maintaining high luminous efficiency, thereby reducing total energy consumption.
Solution Approach 2:
The HOMO energy level parameter is changed across different layers to create a stepped profile. This parameter variation enables the device to operate at lower voltage by providing optimized energy level alignment throughout the structure, reducing the electrical energy input needed while preserving the high conversion efficiency of TADF materials.
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 effectively lowers the driving voltage, prolongs the service life, and reduces energy consumption of the organic electroluminescent device while maintaining high luminous efficiency.
Implementation Method 1
the blue light electron blocking layer is closer to the light-emitting layer than the red light electron blocking layer and the green light electron blocking layer, and an energy level step is introduced in a path of the holes transporting from the anode to the light-emitting layer
Implementation Method 2
triplet excitons may return to singlet through reverse intersystem crossing (Reverse Intersystem Crossing, RISC), forming singlet excitons and then emitting light, thereby improving the radioluminescence efficiency of excitons
Implementation Method 3
When a voltage is applied, electrons from the cathode and holes from the anode will each migrate to the light-emitting layer and are combined to generate excitons, which then emit light with different wavelengths according to the characteristic of the light-emitting layer
Data Source
AI summary
An organic electroluminescent device and a display apparatus, where the organic electroluminescent device includes an anode functional layer, a first electron blocking layer, a second electron blocking layer, a light-emitting layer and a cathode functional layer; the first electron blocking layer includes a red light electron blocking layer and a green light electron blocking layer, which are disposed side by side, and the second electron blocking layer is a blue light electron blocking layer; a HOMO energy level of a red light electron blocking material in the red light electron blocking layer and a HOMO energy level of a green light electron blocking material in the green light electron blocking layer are both lower than a HOMO energy level of a blue light electron blocking material in the blue light electron blocking layer.