OLED Microcavity Color Reproducibility
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Solution Overview
Problem
Organic light emitting devices (OLEDs) face limitations in achieving high color reproducibility due to the use of color filters, which often result in lower color purity compared to the National Television Systems Committee (NTSC) standards, especially as the size of OLEDs increases, making it difficult to deposit emission layers accurately using fine shadow masks.
Innovation Solution
The implementation of microcavity structures in red, green, and blue pixels, where the translucent conductive layers form microcavities with a common electrode, and the use of different transparent conductive layers in each pixel to enhance light emission and color purity, along with a method of manufacturing that includes forming TFTs, passivation layers, and specific conductive layers to optimize the optical path for each color.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If color filters are used to express red, green, and blue colors in each pixel, then the device complexity is reduced and ease of manufacture is improved, but the color reproducibility deteriorates to 72% NTSC
Solution Approach 1:
The patent applies local quality by creating different microcavity structures in different pixel regions. Specifically, red, green, and blue pixels have microcavities with different optical path lengths (d1, d2, d3 respectively) tailored to their specific color requirements. This allows each pixel to have optimized optical properties for its specific color while maintaining a uniform manufacturing process across the entire display.
Solution Approach 2:
The patent changes the optical parameters of the conductive layers by controlling their thickness and refractive index. The translucent conductive layer and transparent conductive layer are deposited with specific thickness ranges (e.g., 50-200 nm for translucent layer) to create the desired microcavity optical path lengths. This parameter control enables high color reproducibility (108.5% NTSC) without requiring color filters.
2Area of stationary object
If the size of OLED increases, then the display area is improved, but the manufacturing precision deteriorates making it difficult to deposit emission layers using fine shadow masks
Solution Approach 1:
The patent extracts and eliminates the fine shadow mask component from the manufacturing process. Instead of using shadow masks to define pixel regions, the invention uses a uniform translucent conductive layer deposited across the entire display area, followed by selective formation of transparent conductive layers in each pixel region. This approach removes the shadow mask constraint that limits display size.
Solution Approach 2:
The patent segments the conductive layer formation process into multiple steps: first forming a uniform translucent conductive layer across the entire display, then selectively forming transparent conductive layers in red, green, and blue pixel regions. This segmentation allows large-area deposition without shadow masks while still achieving precise color differentiation in each pixel.
3Illumination intensity
If translucent conductive layers form microcavities with common electrode, then the light emission intensity is improved, but the device complexity increases
Solution Approach 1:
The patent applies universality by using the common electrode to serve multiple functions: it acts as both the cathode for electron injection and as one mirror of the microcavity resonator. The translucent conductive layer serves dual purposes as both the anode and the other microcavity mirror. This multi-functionality achieves high light emission intensity through microcavity enhancement without adding separate dedicated components.
Solution Approach 2:
The patent merges the electrode functions with the optical cavity functions. The common electrode and translucent conductive layer are combined to form both the electrical contacts and the optical mirrors of the microcavity. This merging reduces the number of separate components needed while achieving both efficient electron injection and enhanced light extraction.
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 approach significantly improves color reproducibility, achieving about 108.5% NTSC color reproducibility, surpassing traditional methods with only white color emission and color filters, which typically reach 72%, while maintaining high light efficiency and intensity.
Implementation Method 1
the translucent conductive layers form microcavities with a common electrode
Implementation Method 2
forming microcavities together with the second electrodes
Implementation Method 3
Electrons injected from one electrode and holes injected from the other electrode are combined in the emission layer to form exitons, and as the exitons discharge energy, the OLED is illuminated
Data Source
AI summary
An organic light emitting device includes first, second, and third pixels each displaying a different color. Each pixel includes a first electrode, a second electrode facing the first electrode, and an emission layer between the first and second electrodes. The first electrodes of the first and second pixels respectively include a first transparent conductive layer and a translucent conductive layer disposed on at least one of lower and upper portions of the first transparent conductive layer and forming microcavities together with the second electrodes, and the first electrode of the third pixel includes a second transparent conductive layer that is different from the first transparent conductive layer and a translucent conductive layer disposed on at least one of upper and lower portions of the second transparent conductive layer and forming a microcavity together with the second electrode.