Organic Electroluminescence Element with Segmented Electrode
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Solution Overview
Problem
Conventional organic electroluminescence elements face issues with uneven brightness and low external quantum efficiency due to the higher sheet resistance of anodes made from ITO films, leading to inferior luminous efficiency and potential for low external quantum efficiency.
Innovation Solution
The organic electroluminescence element features a substrate with a first and second electrode, where the second electrode has openings for light extraction, and a conductive layer is applied over the second electrode, with a carrier injection layer having recesses in the projection domain of the openings, allowing for improved carrier injection and light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If an ITO film is used for the anode to achieve optical transparency, then light can be extracted, but the sheet resistance is high causing large potential gradient and brightness unevenness
Solution Approach 1:
The anode is segmented into a transparent electrode layer and a reflective electrode layer with openings, allowing different regions to serve different functions: the transparent regions enable light extraction while the reflective regions provide low-resistance current paths, resolving the contradiction between light extraction and brightness uniformity
Solution Approach 2:
Different regions of the electrode structure are assigned different properties: the transparent electrode material (ITO) provides optical transparency where needed, while the reflective electrode material (Al, Ag, etc.) provides low electrical resistance in other regions, achieving both light extraction and brightness uniformity simultaneously
2Manufacturing precision
If the anode sheet resistance is reduced to improve brightness uniformity, then brightness unevenness decreases, but optical transparency is compromised
Solution Approach 1:
The electrode is divided into transparent and reflective sections, where the transparent ITO regions maintain optical transparency for light extraction while the reflective metal regions provide low resistance for uniform current distribution, eliminating the need to compromise either property
3Illumination intensity
If a grid electrode with openings is used to improve light extraction, then optical transparency increases, but carrier injection efficiency decreases at opening regions
Solution Approach 1:
The carrier injection layer is designed with locally different thicknesses: thicker regions under the transparent electrode for efficient carrier injection, and thinner or absent regions at the openings for optimal light extraction, allowing each region to optimize its primary function
Solution Approach 2:
The carrier injection layer thickness varies in the vertical dimension to compensate for the horizontal dimension loss of carrier injection area at openings, maintaining overall carrier injection efficiency while preserving light extraction benefits
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 enhances external quantum efficiency and reduces brightness unevenness by optimizing carrier injection and light extraction, resulting in improved luminous efficiency and reduced current concentration.
Implementation Method 1
an organic electroluminescence element including: a substrate; a first electrode arranged on a first surface side of the substrate; a second electrode arranged on the first surface side of the substrate so as to face the first electrode; and a functional layer interleaved between the first electrode and the second electrode, the functional layer including a light emission layer
Implementation Method 2
the second electrode is provided with an opening for extracting light emitted from the functional layer, wherein a conductive layer is formed in the opening so as to be in contact with the second electrode and the functional layer
Data Source
AI summary
Providing an organic electroluminescence element that can reduce the unevenness of the brightness and can improve the external quantum efficiency. The organic electroluminescence element includes a substrate 10, a first electrode 20, a second electrode 40, a functional layer 30 interleaved between the first electrode 20 the second electrode 40 and including a light emission layer 32, and a conductive layer 50. The resistivities of the first electrode 20 and the second electrode 40 are less than the resistivity of transparent conductive oxide. The second electrode 40 has an opening for light extraction. The functional layer 30 includes, as the outermost layer on the second electrode 40 side, a carrier injection layer 34. The conductive layer 50 is optically transparent and is in contact with the second electrode 40 and the functional layer 30. The carrier injection layer 34 has a recess in the projection domain of the opening.