OLED Cathode-Auxiliary Electrode Structure for Uniform Luminance
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Solution Overview
Problem
The increase in electrical resistance of the cathode electrode due to reduced thickness in top emission and dual emission OLEDs leads to luminance non-uniformity and potential power rise (VSS rise phenomenon), along with defects such as deformation, tearing, lifting, and poor contact between the cathode and auxiliary electrodes.
Innovation Solution
A display device structure with an auxiliary electrode and overhang structures in the cathode electrode, including a passivation layer, overcoat layer, and bank layer, to facilitate better contact and reduce electrical resistance, thereby minimizing luminance non-uniformity and defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the thickness of the cathode electrode is decreased to improve transmittance, then the transmittance of the cathode electrode is improved, but the electrical resistance of the cathode electrode increases
Solution Approach 1:
The cathode electrode structure is segmented into multiple layers including a lower cathode electrode layer and an upper cathode electrode layer, with the auxiliary electrode positioned between them. This segmentation allows each layer to be optimized independently - the lower layer can be thinner for transmittance while the upper layer compensates for electrical resistance, resolving the contradiction between transmittance and electrical resistance.
Solution Approach 2:
The auxiliary electrode acts as an intermediary element between the lower and upper cathode electrode layers. It provides additional electrical connection pathways and compensates for the increased resistance caused by thinning the cathode electrode layers, thereby maintaining low electrical resistance while allowing the cathode to be thinner for improved transmittance.
2Illumination intensity
If the thickness of the cathode electrode is decreased to improve transmittance, then the transmittance of the cathode electrode is improved, but luminance non-uniformity occurs due to low-potential power rise
Solution Approach 1:
By segmenting the cathode electrode into multiple layers and introducing the auxiliary electrode, the electrical current distribution is improved. The auxiliary electrode provides additional current pathways that prevent localized potential rises, ensuring uniform luminance across the display while maintaining the thin thickness needed for high transmittance.
Solution Approach 2:
The auxiliary electrode serves as a mediator that distributes electrical potential more evenly across the cathode structure. It prevents the low-potential power rise phenomenon that causes luminance non-uniformity, thereby enabling the use of thinner cathode electrodes for high transmittance without sacrificing luminance uniformity.
3Device complexity
If the cathode electrode and auxiliary electrode contact area is reduced, then the complexity of the structure is reduced, but poor contact and defects such as deformation, tearing, or lifting occur
Solution Approach 1:
The auxiliary electrode is positioned in a vertical dimension between the lower and upper cathode electrode layers, creating a three-dimensional contact structure. This dimensional arrangement provides multiple contact interfaces (lower cathode-auxiliary and auxiliary-upper cathode) without increasing planar complexity, thereby ensuring reliable contact while maintaining structural simplicity.
Solution Approach 2:
The contact structure is segmented into multiple contact interfaces involving the lower cathode electrode, auxiliary electrode, and upper cathode electrode. This segmentation distributes the contact requirements across multiple interfaces, improving overall contact reliability without requiring a large single contact area, thus avoiding deformation, tearing, or lifting defects.
Data Source
AI summary
A cathode electrode is brought into contact with an auxiliary electrode via an undercut defined below an overhang structure, based on a difference between deposition characteristics of an organic light-emitting layer and the cathode electrode, thereby reducing electrical resistance of the cathode electrode. Accordingly, occurrence of low-potential power rise (VSS rise) is reduced due to the reduced electrical resistance of the cathode electrode, such that occurrence of luminance non-uniformity of the display device is reduced.