OLED Capping Layer Thickness Variation for Color Distortion
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Solution Overview
Problem
Organic light emitting diode (OLED) display devices face challenges in light efficiency and color distortion when viewed from different angles, particularly exhibiting a reddish color distortion due to variations in capping layer thickness and refractive index across pixel areas.
Innovation Solution
The OLED display device incorporates a capping layer with varying thickness and refractive index in red, green, and blue pixel areas, along with a red color filter in the red pixel area, to enhance light extraction efficiency and reduce color distortion. The capping layer has specific thickness ranges (30 nm to 150 nm for red and green, and 20 nm to 60 nm for blue) and refractive indices (1.8 to 3.0), and may include refractive-index layers to optimize light emission and color accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform capping layer thickness is used across all pixel areas, then the manufacturing process is simple, but color distortion occurs when viewed from different angles
Solution Approach 1:
The capping layer is designed with different thicknesses for different pixel areas: a first thickness for red and green pixel areas, and a second thickness (greater than the first) for blue pixel areas. This local differentiation compensates for the different emission characteristics of each color, reducing color distortion when viewed from oblique angles while maintaining manufacturability through a controlled deposition process.
2Manufacturing precision
If the capping layer thickness is increased for blue pixel areas, then color distortion is reduced, but the device structure becomes more complex
Solution Approach 1:
The capping layer is designed with different thicknesses for different pixel areas: a first thickness for red and green pixel areas, and a second thickness (greater than the first) for blue pixel areas. This local differentiation compensates for the different emission characteristics of each color, reducing color distortion when viewed from oblique angles while maintaining manufacturability through a controlled deposition process.
3Productivity
If a red color filter is added to the red pixel area, then light extraction efficiency is enhanced, but the device structure and manufacturing process become more complex
Solution Approach 1:
A red color filter is disposed in the red pixel area to enhance light extraction efficiency by matching the emission spectrum of the red organic light emitting layer. This selective color filtering improves the overall luminance and efficiency of the red sub-pixel while maintaining a relatively simple structure by applying the filter only where needed rather than across all pixel areas.
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 significantly enhances light efficiency and minimizes color distortion when viewed from different angles, ensuring consistent color representation across the display.
Implementation Method 1
a capping layer on the second electrode, and having a greater thickness at the red and green pixel areas than a thickness at the blue pixel area
Implementation Method 2
A hole injected from the hole injection electrode and an electron injected from the electron injection electrode are combined with one another within the organic light emitting layer to form an exciton. The OLED element emits light by energy generated when the exciton falls from an excited state to a ground state.
Data Source
AI summary
An organic light emitting diode (OLED) display device includes: a first substrate comprising red, green, and blue pixel areas; a first electrode on the first substrate; red, green, and blue organic light emitting layers on the first electrode at the red, green, and blue pixel areas, respectively; a second electrode on the red, green, and blue organic light emitting layers; a capping layer on the second electrode, and having a greater thickness at the red and green pixel areas than a thickness at the blue pixel area; a thin film encapsulation layer on the capping layer; and a red color filter on the thin film encapsulation layer at the red pixel area.