OLED EL Layer Segmentation for Light Extraction and Reliability
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Solution Overview
Problem
Organic light-emitting devices (OLEDs) face challenges with low light extraction efficiency due to refractive index differences between layers, which affects carrier transport and reliability, making it difficult to form layers with low refractive indices without compromising other critical characteristics.
Innovation Solution
A light-emitting device structure with a first electrode, a second electrode, and an EL layer, where the EL layer has regions with different refractive indices and functions to efficiently extract light while maintaining low current density and improving reliability, including an intermediate layer for hole and electron supply, and specific light-emitting materials for blue, red, and green light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a layer with low refractive index is formed in the EL layer to reduce reflection and improve light extraction efficiency, then light extraction efficiency is improved, but carrier-transport property and reliability deteriorate
Solution Approach 1:
The EL layer is segmented into multiple regions with different refractive indices. The first region has a first refractive index, the second region has a second refractive index lower than the first, and the third region has a third refractive index higher than the second. This segmentation allows each region to contribute differently to light extraction while maintaining overall device reliability through proper material selection and functional distribution.
Solution Approach 2:
Different regions within the EL layer are assigned different refractive index characteristics tailored to their specific functions. The second region with lower refractive index is strategically positioned to maximize light extraction at critical interfaces, while other regions maintain higher refractive indices to ensure proper carrier transport and device reliability. This local optimization resolves the contradiction by applying low refractive index only where it benefits light extraction without compromising overall device performance.
2Reliability
If organic compounds with many unsaturated bonds are used to achieve high carrier-transport property, then carrier-transport property is improved, but refractive index increases
Solution Approach 1:
The EL layer is divided into multiple regions with different organic compound compositions. Regions requiring high carrier transport (such as those with many unsaturated bonds) are segregated from regions where low refractive index is prioritized for light extraction. This spatial segmentation allows each region to optimize its material properties for its specific function without compromising the other.
Solution Approach 2:
The patent employs composite material strategies where different organic compounds with complementary properties are combined in different regions. High-performance compounds with unsaturated bonds for carrier transport are used in regions where transport is critical, while compounds with lower refractive indices are used in regions optimized for light extraction. This composite approach resolves the contradiction by allowing both high carrier transport and low refractive index characteristics to coexist in different parts of the EL layer.
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 structure enables high luminance emission with reduced power consumption and driving voltage, while enhancing reliability and light extraction efficiency, resulting in a more convenient and effective optical functional device.
Implementation Method 1
the attenuation due to reflection which is caused by a difference in refractive index between adjacent layers is a main cause of a reduction in device efficiency
Implementation Method 2
Light-emitting devices (organic EL elements) including organic compounds and utilizing electroluminescence (EL)
Data Source
AI summary
A novel optical functional device that is highly convenient, useful, or reliable is provided. A light-emitting device includes a first electrode, a second electrode, and an EL layer. The first electrode has a first transmittance; the second electrode overlaps with the first electrode. The second electrode has a second transmittance higher than the first transmittance. The EL layer is interposed between the first electrode and the second electrode and includes a first region, a second region, and a third region. The first region is interposed between the second region and the third region. The second region is interposed between the first electrode and the first region and has a first refractive index. The third region is interposed between the first region and the second electrode and has a second refractive index. The second refractive index is lower than the first refractive index. The EL layer includes a first unit, a second unit, and an intermediate layer. The intermediate layer is interposed between the first unit and the second unit and has a function of supplying a hole to one of the first unit and the second unit and supplying an electron to the other.