OLED Pixel Layer Segmentation for Leakage Current Control
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Solution Overview
Problem
Organic light emitting display devices face challenges in achieving optimal light emitting efficiency due to horizontal leakage currents caused by high mobility charged carriers in the hole injection and transport layers, leading to decreased efficiency in certain colors, particularly green, and difficulties in expressing gray scale and colors.
Innovation Solution
The use of a second layer with higher hole injectivity than the first layer, which includes a charge generating material, is sequentially deposited over pixel regions, and is electrically or physically independent across adjacent pixels to prevent leakage currents, ensuring optimal light emitting efficiency across all colors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a material having a charged carrier with high mobility is used in the hole injection layer and hole transport layer, then power consumption is decreased and efficiency is increased, but horizontal leakage current is generated causing adjacent pixels to light up and color expression to deteriorate
Solution Approach 1:
The hole injection layer and hole transport layer are divided into separate layers rather than using a single common layer. This segmentation allows each layer to have optimized material properties - the hole injection layer can use high mobility materials for efficient charge injection, while the hole transport layer can be designed to prevent lateral charge transport, thereby eliminating horizontal leakage current between adjacent pixels while maintaining low power consumption
Solution Approach 2:
Different material properties are assigned to different layers based on their specific functions. The hole injection layer uses materials with high charge carrier mobility for efficient charge injection, while the hole transport layer uses materials with appropriate mobility characteristics to transport holes vertically without lateral leakage, achieving local optimization of material properties to resolve the contradiction between power efficiency and color accuracy
2Ease of manufacture
If the hole injection layer and hole transport layer are formed from a common layer over all pixels, then manufacturing is simplified, but horizontal leakage current occurs preventing proper gray scale and color expression
Solution Approach 1:
The previously common layer structure is segmented into separate hole injection layer and hole transport layer. This segmentation enables precise control over charge transport characteristics in each layer, preventing horizontal leakage current and achieving accurate color and gray scale expression, while still maintaining a relatively simple manufacturing process through sequential deposition
3Device complexity
If the hole injection layer and hole transport layer are formed in the same location independent of pixel characteristics, then device structure is simplified, but light emitting efficiency varies significantly among different colors with green showing decreased efficiency
Solution Approach 1:
The layer structure is optimized with local quality considerations - the hole injection layer and hole transport layer are designed with specific material properties and thicknesses tailored to the light emitting characteristics of each pixel type. This allows red and blue pixels to achieve high efficiency at their optimal locations while green pixels, which emit near the electron transport layer, also achieve optimal efficiency through the optimized layer structure, ensuring uniform high efficiency across all colors
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 solution enhances light emitting efficiency while operating at low voltage, prevents leakage currents, and allows for excellent gray expression even in low luminance, ensuring uniform light emitting locations across all pixels.
Implementation Method 1
The second layer may include a charge generating material
Data Source
AI summary
An organic light emitting display device that can reach the optimum light emitting efficiency of each pixel while operating at a low voltage. The organic light emitting display device includes a first pixel region emitting a first color, a second pixel region emitting a second color different from the first color, a first layer formed over the first and second pixel regions, and having at least one of a hole injection layer and a hole transport layer, and a second layer formed over the first and second pixel regions, and having hole injectivity higher than the first layer, wherein the first and second layers are sequentially deposited in the first pixel region, and the second and first layers are sequentially deposited in the second pixel region.