Light Emitting Element with Hole Generating Layer
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Solution Overview
Problem
Thin film light-emitting elements with multilayer structures face challenges in reducing drive voltage and preventing its increase over time, leading to higher power consumption and reduced reliability due to limited electron-injecting materials and high electron injection resistance from electrodes.
Innovation Solution
Incorporating a hole-generating layer and an electron-generating layer between the electrodes, with a light-emitting layer in between, using materials like P-type and N-type semiconductors and organic compounds to optimize molar ratios and thicknesses to reduce drive voltage and stabilize it over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a multilayer structure with hole-injecting layer, hole-transporting layer, electron-transporting layer, and electron-injecting layer is used, then light emission efficiency is improved, but drive voltage becomes high and increases over time
Solution Approach 1:
The patent introduces a hole-generating layer as an intermediary between the electrode and the light-emitting stack. This layer generates holes that are injected into the light-emitting layer, eliminating the need for direct electron injection from the electrode into organic compound layers. The hole-generating layer acts as a mediator that converts electron injection into hole injection, thereby reducing the drive voltage while maintaining efficient light emission.
Solution Approach 2:
The patent changes the fundamental parameter of charge carrier type injected from the electrode. Instead of injecting electrons directly into organic compound layers (which requires high voltage), the system injects electrons into the hole-generating layer and converts them to holes through chemical reactions. This parameter change from electron injection to hole injection significantly reduces the required drive voltage.
2Reliability
If materials with good electron-injecting properties are used, then electron injection efficiency is improved, but the number of available materials is very limited
Solution Approach 1:
The hole-generating layer serves as an intermediary that decouples the electrode material selection from the organic compound layer material selection. The electrode only needs to provide good electron injection into the hole-generating layer, while the organic compound layers can be selected based on their hole-transporting and light-emitting properties. This intermediary structure dramatically expands material selection flexibility.
Solution Approach 2:
The patent segments the electron injection function from the organic compound layer functions. The hole-generating layer handles electron injection and hole generation, while separate organic compound layers handle hole transport and light emission. This functional segmentation allows independent optimization of each layer's materials.
3Speed
If electron injection from electrode into organic compound layer is attempted, then direct electron supply to light-emitting layer is achieved, but injection is rare to occur and drive voltage is high
Solution Approach 1:
The patent introduces the hole-generating layer as an intermediary medium between the electrode and the organic compound layers. Electrons are first injected into this layer, where they chemically react to generate holes. These holes are then transported to the light-emitting layer. This intermediary mechanism transforms a difficult electron injection process into a more favorable hole injection and transport process.
Solution Approach 2:
The patent replaces the direct mechanical/electrical electron injection mechanism into organic compounds with a chemical reaction mechanism. Electrons injected into the hole-generating layer undergo chemical reactions to produce holes, which are then transported to the light-emitting layer. This substitution of injection mechanism significantly improves injection efficiency and reduces voltage requirements.
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 solution effectively lowers the drive voltage and slows its increase, improving the reliability and longevity of the light-emitting element by alleviating stress on the light-emitting layer and enhancing electron injection efficiency.
Implementation Method 1
a first layer and a second layer each containing an organic material and an inorganic material... a fourth layer generating electrons
Implementation Method 2
a third layer containing a light emitting material... which emits light when current is applied
Data Source
AI summary
It is an object of the present invention to provide a light-emitting element having a structure in which the drive voltage is relatively low. Further, it is an object of the invention to provide a highly reliable light emitting device by alleviating the stress to the light emitting layer. Further, it is another object of the invention to provide a light emitting element having a structure in which increase in the drive voltage over time is small. It is an object of the present invention to provide a display device in which the drive voltage is low and increase in the drive voltage over time is small and which can withstand long-term use. In a light emitting element, a layer in contact with an electrode serves as a hole generating layer such as an organic compound layer containing a P-type semiconductor or an electron accepting material, a light emitting layer is provided between hole generating layers, an electron generating layer is formed between the hole generation layer on the cathode side and the light emitting layer.