Organic Electroluminescence Device Hole Transporting Zone Refractive Index Optimization
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Solution Overview
Problem
Organic electroluminescence devices face low light-extraction efficiency due to refractive index differences between layers, leading to significant light emission loss.
Innovation Solution
Incorporating a hole transporting zone with a first anode side organic layer and a second anode side organic layer, where the first layer has a higher refractive index than the second layer, and a total film thickness between 20 nm to 80 nm, to reduce light emission loss by optimizing the refractive index difference and layer thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single organic layer is used in the hole transporting zone, then the device structure is simple, but light-extraction efficiency is low due to refractive index differences between layers
Solution Approach 1:
The hole transporting zone is divided into multiple organic layers (first hole transporting layer, second hole transporting layer, third hole transporting layer) with different refractive indices. This segmentation allows optimization of light extraction by creating refractive index gradients that reduce total internal reflection at interfaces, thereby reducing light emission loss while maintaining manageable structural complexity.
Solution Approach 2:
Each organic layer in the hole transporting zone is assigned specific local properties (different refractive indices, different thicknesses) tailored to its position. The first layer near the anode has one set of properties, while subsequent layers have optimized properties for their respective locations, enabling localized optimization of both light extraction and hole transport functions.
2Loss of energy
If the organic layer thickness is increased to improve light extraction, then light-extraction efficiency improves, but the device thickness increases
Solution Approach 1:
The total thickness required for effective light extraction is segmented across multiple layers. Each layer has an optimized thickness (e.g., first layer: 5-20 nm, second layer: 10-30 nm, third layer: 15-40 nm) that contributes to overall light extraction efficiency without requiring any single layer to be excessively thick, thus controlling overall device thickness.
Solution Approach 2:
The hole transporting zone uses composite organic layer structures with different material compositions and refractive indices. This composite approach enables effective light extraction through refractive index matching and gradient effects while maintaining a compact overall thickness, as each material contributes specific optical and electrical properties.
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
Enhances light-extraction efficiency by minimizing losses in both evanescent and thin film modes, improving the overall luminous efficiency of the organic electroluminescence device.
Implementation Method 1
decay due to the reflection caused by the difference between refractive indices of adjacent layers is a major factor in reducing the light-extraction efficiency
Implementation Method 2
decay due to the reflection caused by the difference between refractive indices of adjacent layers
Implementation Method 3
When a voltage is applied to the organic EL device, holes are injected from an anode and electrons are injected from a cathode into an emitting layer. The injected electrons and holes are recombined in the emitting layer to form excitons.
Data Source
AI summary
An organic electroluminescence device includes: an emitting region provided between a cathode and an anode; and a hole transporting zone provided between the anode and the emitting region, in which the hole transporting zone includes at least a first anode side organic layer and a second anode side organic layer, the first anode side organic layer is in direct contact with the second anode side organic layer, a total film thickness of the hole transporting zone is in a range from 20 nm to 80 nm, the first anode side organic layer contains no compound contained in the second anode side organic layer, the first anode side organic layer contains a first organic material and a second organic material, the first organic material is different from the second organic material, and a content of the first organic material in the first anode side organic layer is less than 50 mass %.