OLED Positive Electrode Structure for Uniform Light Emission
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Solution Overview
Problem
Active matrix type OLED displays face challenges with non-uniform semiconductor layer formation due to difficulties in achieving uniform crystallization, leading to defective light emission characteristics, especially as display size increases.
Innovation Solution
The OLED display employs an inverted structure with an n-type TFT and a positive electrode comprising an auxiliary layer, a conductive layer, and an insulation layer, which are sequentially formed through thermal evaporation to enhance hole injection and reduce resistance, thereby improving luminous efficiency and preventing non-uniform luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type TFT with polycrystalline silicon semiconductor layer is used, then the positive electrode can be connected with the TFT, but uniform crystallization is difficult to achieve, resulting in non-uniform light emission characteristics
Solution Approach 1:
The patent inverts the conventional connection structure by connecting the negative electrode to the TFT instead of the positive electrode. This allows the use of an n-type TFT with amorphous or microcrystalline semiconductor layer, eliminating the difficult crystallization process while maintaining device functionality. The inverted structure resolves the contradiction by achieving reliable operation without requiring uniform crystallization.
Solution Approach 2:
The patent changes the semiconductor layer parameters from polycrystalline (requiring high-temperature crystallization) to amorphous or microcrystalline (formable at lower temperatures). This parameter change enables uniform film formation without the crystallization uniformity problems, thereby improving light emission uniformity while simplifying manufacturing.
2Area of stationary object
If the OLED display size is increased, then the display area is improved, but the non-uniform semiconductor layer problem becomes more serious
Solution Approach 1:
By inverting the electrode-TFT connection structure, the patent enables the use of n-type TFTs with amorphous or microcrystalline semiconductor layers that can be formed uniformly over large areas without requiring high-temperature crystallization processes. This resolves the contradiction by allowing large display areas to be manufactured with uniform semiconductor layers.
3Reliability
If thermal evaporation is used to form the positive electrode layers, then hole injection is enhanced and resistance is reduced, but the organic emission layer may be damaged
Solution Approach 1:
The patent changes the deposition parameters by using thermal evaporation at controlled temperatures and rates, forming the auxiliary layer, conductive layer, and insulation layer with specific thicknesses (auxiliary layer: 5-50 nm, conductive layer: 10-30 nm). These parameter controls allow effective hole injection and resistance reduction while preventing damage to the organic emission layer through optimized deposition conditions.
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 light emission characteristics and luminous efficiency by facilitating hole injection, reducing resistance, and preventing voltage drops, resulting in improved panel luminance and transmittance without damaging the organic emission layer.
Implementation Method 1
an auxiliary layer, a conductive layer, and an insulation layer which are sequentially formed through thermal evaporation
Data Source
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AI summary
An organic light emitting diode (OLED) display (101) includes a substrate (111) including a plurality of pixels defined thereon, a thin film transistor (20) positioned at each pixel, a negative electrode (710) electrically connected to the thin film transistor (20), an organic emission layer (720) positioned on the negative electrode (710), and a positive electrode (730) positioned on the organic emission layer (720), the positive electrode (730) including an auxiliary layer (732, 733) positioned on the organic emission layer (720), a conductive layer (734) positioned on the auxiliary layer (732, 733), and an insulation layer (736) positioned on the conductive layer (734).