Top Emission OLED With Auxiliary Electrode for High Luminance
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Solution Overview
Problem
Organic light emitting elements, particularly those using a bottom emission system, face issues with low aperture ratio due to the presence of light-absorbing TFTs and electrodes, leading to reduced luminance and shorter lifespan, especially in high-definition displays where high voltage application accelerates deterioration.
Innovation Solution
The introduction of a top emission organic light emitting element design with a transparent conductive second electrode and an auxiliary electrode on a wider wall-like insulating layer, which reduces surface resistance and allows for uniform voltage application, enhancing luminance and aperture ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a bottom emission organic light emitting element is used with TFTs and electrodes made of light-absorbing materials, then the device can be manufactured with conventional materials and processes, but the aperture ratio is low and luminance is reduced
Solution Approach 1:
The patent inverts the light emission direction from bottom emission to top emission. The second electrode is made transparent to light and the first electrode reflects light, so that light generated in the organic light emitting layer is output from the second electrode side opposite to the substrate side where the TFTs and electrodes are provided. This inversion allows the light path to avoid the light-absorbing TFTs and electrodes, thereby increasing the aperture ratio and luminance while maintaining ease of manufacture with conventional materials.
2Illumination intensity
If high voltage is applied to pixels to achieve high luminance in PM organic EL elements, then instantaneous luminance is improved, but the light emitting layers deteriorate rapidly and lifespan is reduced
Solution Approach 1:
The patent changes the drive system parameter from passive matrix (PM) to active matrix (AM) driving. In the AM drive system, switching elements (TFTs) are provided for the respective pixels, allowing switching among pixels and enabling every pixel to be driven at almost 100% performance for a single frame. This parameter change reduces the instantaneous voltage required compared to PM driving, thereby reducing deterioration of the light emitting layers and extending lifespan while maintaining high luminance capability.
3Illumination intensity
If a transparent conductive material is used for the second electrode to enable top emission, then light transmittance is improved and aperture ratio is increased, but surface resistance becomes high and uniform voltage application becomes difficult
Solution Approach 1:
The patent employs a composite electrode structure where the second electrode is formed of transparent conductive material (such as ITO or IZO) that provides high light transmittance. This transparent conductive material layer is combined with an auxiliary electrode structure to compensate for the high surface resistance. The composite structure allows the transparent electrode to maintain its light-transmitting function while the auxiliary electrode provides additional conductive pathways to ensure uniform voltage distribution across the electrode surface.
4Illumination intensity
If the aperture ratio is increased to improve luminance, then more light can be emitted, but the area available for TFTs and electrodes is reduced, complicating the device structure
Solution Approach 1:
The patent resolves the aperture ratio conflict by changing the light emission dimension from bottom emission (through the substrate) to top emission (through the second electrode). This dimensional change in light output direction allows the light-emitting area to be maximized without compromising the functional area for TFTs and electrodes on the substrate side. The first electrode is designed to reflect light upward, and the second electrode is made transparent, creating an effective light output path that increases aperture ratio while maintaining standard TFT and electrode configurations.
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 top emission design enables high luminance and uniform image display with reduced variations, extending the lifespan of organic light emitting elements by minimizing voltage drop and maintaining color balance over time.
Implementation Method 1
The holes implanted from the first electrode 602 and the electrons implanted from the second electrode 604 are recombined in the organic light emitting layer 603, whereby light emission occurs in the organic light emitting layer 603.
Data Source
AI summary
An organic EL element includes a substrate, a plurality of first electrodes which are arranged on the substrate in a matrix configuration, a wall-like insulating layer which is formed on the substrate, organic light emitting layers which are formed on the first electrodes, respectively, an auxiliary electrode which is formed on top of the wall-like insulating layer and a second electrode which is formed to cover the surfaces of the wall-like insulating layer, the auxiliary electrode and the light emitting layers and electrically connected to the auxiliary electrode. The second electrode is transparent to light from the light emitting layers.