OLED Microcavity Thickness Ratios for Inkjet Productivity
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Solution Overview
Problem
The existing methods for forming an emitting layer in OLED display devices, such as vacuum thermal evaporation and inkjet methods, face challenges in achieving the required thickness for a microcavity effect while maintaining high productivity and resolution, especially for large-sized substrates and high-resolution displays above 250 PPI, due to limitations in material distribution and drying times.
Innovation Solution
The OLED display device employs a substrate with pixel regions having specific thickness ratios of upper electrodes to organic light emitting layers, allowing for reduced number of drops and improved productivity through the inkjet method, with the upper electrode thickness ranging from 1:3 to 1:4 for the first light emitting element, 1:2.5 to 1:3 for the second, and 1:1.5 to 1:2 for the third, enabling efficient microcavity effect formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the vacuum thermal evaporation method using shadow mask is used to form the emitting layer, then the emitting layer can be formed with controlled thickness, but the method becomes difficult to apply to large-sized substrates and high-resolution displays over 250 PPI due to shadow mask sagging and deterioration
Solution Approach 1:
The patent replaces the mechanical shadow mask system with a photomask-based photolithography system. The photomask is a flat, rigid structure that can be easily manufactured for high-resolution patterns (over 250 PPI) and large substrate sizes without the sagging and deterioration issues that plague flexible shadow masks. The photolithography process uses light to transfer the pattern from the photomask to the photoresist layer, enabling precise control of emitting layer thickness and pattern while being adaptable to large-area and high-resolution displays.
2Ease of manufacture
If the inkjet method is used to form the emitting layer, then material waste is prevented and maintenance is easier, but the emitting layer thickness required for microcavity effect cannot be achieved by a single drop and requires multiple drops with long drying times
Solution Approach 1:
The patent modifies the parameters of the inkjet printing process by adjusting the concentration, viscosity, and formulation of the emitting material solution to enable sufficient thickness accumulation in fewer drops. The drying conditions (temperature, humidity, air flow) are also optimized to reduce drying time between drops. These parameter changes allow the emitting layer to reach the required thickness for microcavity effect with reduced number of drops and shorter drying times, thereby improving productivity while maintaining the material efficiency and ease of maintenance advantages of the inkjet method.
3Manufacturing precision
If multiple drops are used in the inkjet method to achieve the required emitting layer thickness, then the microcavity effect can be achieved, but the number of drying steps increases and productivity per hour decreases
Solution Approach 1:
The patent prepares the emitting material solution in advance with optimized concentration and additives that promote faster solvent evaporation and better material distribution. The substrate temperature and ambient drying conditions are pre-adjusted to accelerate the drying process. By performing these preliminary preparations, the patent reduces the time required for each drying step, allowing multiple drops to be applied more quickly while still achieving the required emitting layer thickness for the microcavity effect, thus maintaining productivity.
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 allows for the formation of emitting layers with the necessary thickness for a microcavity effect while reducing the number of drops and drying time, enhancing productivity and maintaining high emission efficiency and color reproducibility, thus overcoming the limitations of previous methods.
Implementation Method 1
an organic light emitting diode (OLED) display device has superior properties such as high luminance and low driving voltage. The OLED display device uses an emissive electroluminescent layer to realize a high contrast ratio
Implementation Method 2
the distances between the first and second electrodes are different from each other in red, green and blue pixel regions for improving a color purity of red, green, and blue and for increasing emission efficiency due to a microcavity effect
Data Source
AI summary
An organic electroluminescent device includes a substrate having a plurality of pixel regions defined thereon; and, in each pixel region, at least first, second and third light emitting elements formed on the substrate, each of the first, second, and third light emitting elements including a lower first electrode, an upper first electrode, an organic-light emitting layer, and a second electrode. A ratio of a thickness of the upper first electrode to a thickness of the organic light emitting layer in the first light emitting element is 1:3 to 1:4. A ratio of a thickness of the upper first electrode to a thickness of the organic light emitting layer in the second light emitting element is 1:2.5 to 1:3. A ratio of a thickness of the upper first electrode to a thickness of the organic light emitting layer in the third light emitting element is 1:1.5 to 1:2.