Transparent Electrodes Boost OLED Opening Ratio
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Solution Overview
Problem
Conventional organic light emitting display devices have a reduced opening ratio due to the presence of opaque electrode layers in the pixel circuit, which obstruct light emission and are further compromised by the addition of compensating circuits in each sub-pixel.
Innovation Solution
The use of transparent conductive layers and opaque conductive layers in a stacked structure for the source and drain electrodes, along with a transparent storage capacitor, allows light to be emitted from both regions where the pixel circuit is and is not present, thereby increasing the opening ratio and enabling high-resolution displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If opaque electrode layers are used in the pixel circuit, then the pixel circuit can be formed with proper electrical conductivity, but the opening ratio is reduced due to light obstruction
Solution Approach 1:
The electrode layers are designed with spatially varying optical properties: the first source electrode and first drain electrode use transparent conductive layers in the first light emitting region to maintain conductivity while allowing light transmission, whereas the second source electrode and second drain electrode use opaque conductive layers in the second light emitting region where light emission is not required. This local differentiation resolves the contradiction between electrical conductivity and light transmission.
Solution Approach 2:
The invention introduces a dual-region structure that divides the light emitting region into a first light emitting region (where pixel circuit is present) and a second light emitting region (where pixel circuit is not present). By assigning different material properties to electrodes in different regions, the patent adds a spatial dimension to the electrode design, allowing simultaneous optimization for both conductivity and light emission in respective zones.
2Reliability
If compensating circuits are added to each sub-pixel, then display performance is improved, but the opening ratio becomes even more difficult to secure
Solution Approach 1:
The storage capacitor, which is part of the compensating circuit, is designed with a transparent conductive layer as its lower electrode in the first light emitting region. This allows the compensating circuit to function properly while maintaining light transmission capability in the region where it is disposed, thereby improving display performance without sacrificing opening ratio.
3Area of stationary object
If transparent conductive layers are used in electrode structures, then light emission is improved, but manufacturing complexity increases
Solution Approach 1:
The patent divides the electrode structure into multiple segments with different material compositions: transparent conductive layers (such as ITO, IZO, or ZnO) are used specifically in the first light emitting region where light emission is required, while opaque conductive layers are used in the second light emitting region. This segmentation allows the use of transparent materials only where necessary, minimizing manufacturing complexity while maximizing light emission benefit.
Data Source
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Figure 3A~3B
AI summary
Disclosed are an organic light emitting display device improving opening ratio and a method of fabricating the same. The organic light emitting display device includes a light emitting device (130) disposed at each sub-pixel of a substrate (101), a pixel circuit driving the light emitting device (130), a bank (138) in which a first opening provides a first light emitting region (EA1) at a remaining region except for a region where the pixel circuit is disposed, and in which a second opening provides a second light emitting region (EA2) at the region where the pixel circuit is disposed, and a color filter (160) disposed below the first and second light emitting regions (EA1, EA2), wherein at least one of electrodes included in the pixel circuit includes a transparent conductive layer (172a) at the second light emitting region (EA2).