OLED Substrate Pixel Defining Layer Asymmetry
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Solution Overview
Problem
In organic light emitting display substrates, the 'coffee ring effect' causes a thicker film layer at the peripheral region, leading to uneven light emission, with the central region being brighter and the peripheral region darker due to solvent evaporation and ink flow during the manufacturing process, resulting in non-uniform display effects.
Innovation Solution
The design includes a first pixel defining layer with openings and a second pixel defining layer where the edges of the second openings extend outward to expose portions of the first layer, creating a difference in length greater than width, which reduces the contact area between the film layer and the pixel electrode, thereby minimizing the dark regions and enhancing light uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ink is inkjet printed into the accommodation groove to form a film layer, then the light emitting unit is formed, but the solvent evaporation causes ink to flow from central region to peripheral region, resulting in non-uniform film thickness and coffee ring effect
Solution Approach 1:
The pixel defining layer is divided into multiple regions with different opening sizes: first openings in the first pixel defining layer and second openings in the second pixel defining layer. The second openings have different dimensions (length difference greater than width difference) to create multiple accommodation grooves with varying volumes, allowing differential ink distribution that compensates for the coffee ring effect and achieves uniform film thickness across the light emitting unit.
Solution Approach 2:
Different regions of the pixel defining layer are designed with locally optimized opening characteristics. The first and second openings have different size variations, creating local differences in accommodation groove volume. This local quality variation ensures that ink distributed across different regions forms film layers of uniform thickness, counteracting the peripheral accumulation caused by solvent evaporation.
2Quantity of substance
If the peripheral region of the film layer has greater thickness, then more ink is deposited at the periphery, but this creates dark display regions in the peripheral area, reducing display uniformity
Solution Approach 1:
The second openings are designed with asymmetric dimension changes where the length difference between first and second openings is greater than the width difference. This asymmetric design creates accommodation grooves with optimized volume distribution, controlling ink flow and deposition to achieve uniform film thickness and eliminate the asymmetric dark regions that normally appear at the peripheral areas of the display.
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 reduces the width of dark regions, increases light uniformity, and improves the display effect by separating more of the peripheral film layer from the pixel electrode, ensuring a more consistent brightness across the display substrate.
Implementation Method 1
since a solvent of the ink mostly evaporates from the peripheral region of a layer of the ink, the ink will flows from the central region of the layer of the ink to the peripheral region
Data Source
AI summary
An organic light emitting display substrate comprises a substrate, a first pixel defining layer provided on the substrate and a second pixel defining layer provided on the first pixel defining layer. The first pixel defining layer includes a plurality of first openings, and the second pixel defining layer includes a plurality of second openings in one-to-one correspondence with the plurality of first openings. An edge of each of the plurality of second openings extends outwards beyond an edge of the corresponding first opening so as to expose a portion of the first pixel defining layer, and a difference in length between each of the plurality of second openings and the corresponding first opening is greater than a difference in width between the second opening and the corresponding first opening.