Undercoat Layer for Drop-Dispensed Electron Transport Layers
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Solution Overview
Problem
Display devices with light-emitting elements, such as OLEDs and QLEDs, face issues with insufficient display capability when the light-emitting layer is formed by dropwise dispensing.
Innovation Solution
A display device structure that includes a substrate, thin film transistor layer, light-emitting element layer, and sealing layer, with an undercoat layer between the cathode and electron transport layer, using oxide nanoparticles and a binder resin, and a common or insular electrode configuration to enhance binding and prevent medium dissolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the light-emitting layer is formed by dropwise dispensing, then the manufacturing process is simplified and productivity is improved, but the display capability becomes insufficient
Solution Approach 1:
An undercoat layer is introduced as an intermediary between the cathode and the electron transport layer. This undercoat layer serves as a mediator that prevents the medium from the dropwise dispensing process from dissolving the electron transport layer, thereby enabling the use of dropwise dispensing (high productivity) while maintaining display quality (manufacturing precision).
Solution Approach 2:
The undercoat layer is formed in advance before the electron transport layer is deposited. This preliminary action prepares the surface and creates a protective barrier that prevents subsequent dissolution issues, allowing the electron transport layer to be formed with good adhesion and preventing medium from penetrating and dissolving it during the dropwise dispensing process.
2Reliability
If an electron transport layer containing oxide nanoparticles and binder resin is used, then the light-emitting element performance is improved, but the layer may be dissolved by the medium during dropwise dispensing
Solution Approach 1:
The undercoat layer acts as a protective intermediary that shields the electron transport layer from direct contact with the dispensing medium. This prevents the medium from dissolving the binder resin and nanoparticles in the electron transport layer, maintaining its compositional stability while allowing the layer to perform its light-emitting function reliably.
Solution Approach 2:
The undercoat layer provides beforehand cushioning or protection to the electron transport layer against the harmful effect of medium dissolution. By placing this protective layer in advance, the electron transport layer's composition is protected from degradation, ensuring both performance and stability.
3Device complexity
If a common electrode is used for multiple light-emitting elements, then the device structure is simplified and manufacturing is easier, but the binding between layers may be insufficient
Solution Approach 1:
The undercoat layer serves as an intermediary that enhances the binding between the cathode and the electron transport layer. Even when a common electrode structure is used (simplifying device complexity), the undercoat layer ensures strong adhesion and prevents delamination, thereby maintaining layer binding strength without requiring more complex electrode configurations.
Data Source
AI summary
A display device has a display area in which there is provided a plurality of pixels and a frame area surrounding the display area. The display device includes, in the display area; a substrate; a thin film transistor layer; a light-emitting element layer including a plurality of light-emitting elements configured to emit light of mutually different colors; and a sealing layer in this order. The plurality of light-emitting elements include a cathode, an electron transport layer, a light-emitting layer, a hole transport layer, and an anode in this order from a substrate side. The electron transport layer includes oxide nanoparticles and a binder resin. On an electron transport layer side of the cathode, there is provided an undercoat layer in contact with the electron transport layer.