OLED Upper Electrode Resistance via Conductive Organic Layer
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Solution Overview
Problem
Existing organic electroluminescence display devices face challenges in achieving low resistance for the upper electrode across the entire display area without complicating the manufacturing process, leading to uneven luminance between the edge and central portions of the display area.
Innovation Solution
The use of a conductive inorganic lower electrode, a light-emitting organic layer with multiple organic material layers, a conductive inorganic upper electrode covering the entire display area, and a conductive organic layer that can include a charge generation layer and ions, along with a sealing film made of inorganic materials, to planarize irregularities and reduce resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the upper electrode is made thinner to improve light transmittance, then light transmittance is improved, but resistance value rises and voltage drop occurs causing luminance unevenness
Solution Approach 1:
The upper electrode is constructed as a composite structure with a first upper electrode layer (transparent conductive oxide like ITO) and a second upper electrode layer (conductive organic material like PEDOT:PSS or metal nanoparticles). This composite structure combines the high transparency of the first layer with the low resistance of the second layer, achieving both improved light transmittance and reduced resistance simultaneously.
2Reliability
If a routed wiring is provided in the non-display area to achieve low resistance, then resistance is reduced, but the manufacturing process becomes complicated
Solution Approach 1:
The second upper electrode layer made of conductive organic material serves multiple functions: it reduces the resistance of the upper electrode, acts as an intermediate layer between the transparent conductive oxide and the organic light-emitting layer, and can be formed in a single step across the entire display area using conventional coating methods, thereby simplifying the manufacturing process while achieving low resistance.
3Illumination intensity
If two or more light-emitting layers of different colors are stacked, then color emission is improved, but an intermediate connection layer must be provided complicating the structure
Solution Approach 1:
The conductive organic material layer serves as an effective intermediary between stacked light-emitting layers of different colors, providing both electrical connection and charge injection functionality. This single intermediate layer simplifies the overall structure compared to traditional designs that would require separate connection layers for each interface between light-emitting layers.
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 achieves low resistance for the upper electrode, improves conductivity, and enhances image quality by maintaining potential across the cathode, even in bright screens requiring large currents, while simplifying the manufacturing process and preventing moisture ingress.
Implementation Method 1
a conductive organic layer that is in contact with the upper electrode, formed so as to cover the whole of the display area, and made of a conductive organic material
Implementation Method 2
a light-emitting organic layer that is in contact with the lower electrode and made of a plurality of different organic material layers including a light-emitting layer emitting light
Data Source
AI summary
An organic electroluminescence display device includes: a lower electrode that is made of a conductive inorganic material and formed in each of pixels arranged in a matrix in a display area; a light-emitting organic layer that is in contact with the lower electrode and made of a plurality of different organic material layers including a light-emitting layer emitting light; an upper electrode that is in contact with the light-emitting organic layer, formed so as to cover the whole of the display area, and made of a conductive inorganic material; and a conductive organic layer that is in contact with the upper electrode, formed so as to cover the whole of the display area, and made of a conductive organic material.