Conductive Foil Substrate for Large-Area OLED Luminance
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Solution Overview
Problem
Current organic light-emitting diode (OLED) devices with flexible substrates face limitations in achieving uniform luminance over large areas due to high sheet resistance of electrodes, which restricts the maximum light-emitting area and requires expensive thin-film deposition techniques, while top-emitters are further constrained by optical and process temperature considerations.
Innovation Solution
An organic electroluminescent device with a conductive foil substrate featuring a first metal layer with a sheet resistance of less than 0.05 Ω/square, a transparent top electrode, and a protection element, allowing for reduced voltage drop and homogeneous luminance across large areas, achieved through the use of thick metal layers or highly conductive materials like gold, silver, or copper, and a second metal area for direct electrical contact to the top electrode, along with a diffusion barrier layer to prevent degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If common thin-film electrodes with high sheet resistance (≥0.1 Ω/square) are used, then the device structure is simple and manufacturing is easy, but the maximum light-emitting area is limited to a few tens of square cm and luminance uniformity deteriorates
Solution Approach 1:
The device divides the large light-emitting area into multiple sub-tiles, each with its own low-ohmic contact area. This segmentation allows each sub-tile to have sufficient current injection while collectively achieving large total emitting area with uniform luminance across the entire device.
Solution Approach 2:
The invention introduces a vertical dimension by creating low-ohmic contact areas that extend from the substrate through the organic layers to the top electrode. This three-dimensional contact structure reduces sheet resistance effects by providing multiple current injection paths through the thickness of the device.
2Illumination intensity
If ITO is used as top electrode in top-emitters, then optical requirements are met, but electrical parameters are compromised by process temperature restrictions and the size limitation is even more severe
Solution Approach 1:
The top electrode is segmented into light-emitting areas and separate low-ohmic contact areas. This allows the ITO layer to be optimized for optical performance in the light-emitting regions while the contact areas provide the necessary electrical conductivity without compromising the optical characteristics of the main emitting surfaces.
3Area of stationary object
If OLED is subdivided into sub-tiles to increase total light-emitting area, then the individual electrode size is reduced, but metal tracks are required for interconnection and track resistance should be well below 0.01 Ohm/square
Solution Approach 1:
The invention merges the electrode function with the substrate by creating low-ohmic contact areas that are integrally formed with the organic layers and electrodes. This eliminates the need for separate metal track interconnections between sub-tiles, as each sub-tile is electrically connected through its own low-ohmic contact area formed during the same deposition process.
4Area of stationary object
If thin-film technology is used for large-area solutions, then the device can be manufactured, but the resistance of thin layers is too high and producing sufficiently thick layers is expensive and time consuming
Solution Approach 1:
The invention changes the thickness parameter of the metal layers in the low-ohmic contact areas to achieve the required conductivity. By depositing thicker metal layers (or using highly conductive materials) in the contact areas specifically, the sheet resistance is reduced to well below 0.01 Ω/square without requiring expensive alternative technologies, maintaining compatibility with standard vacuum deposition processes.
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
The solution enables large-area OLEDs with homogeneous luminance and extended operational life, facilitating production with lower effort and allowing for flexible and curved light sources, while reducing ohmic losses and improving luminance homogeneity by distributing driving current close to the light-emitting area.
Implementation Method 1
a first metal layer with a thickness such as to result in a sheet resistance of less than 0.05 Ω/square on the upper side of the carrier material, the latter comprising at least a first metal area as a bottom electrode
Implementation Method 2
an organic layer stack deposited on top of the bottom electrode designed to emitting light
Implementation Method 3
The first metal layer further comprises a conductive diffusion barrier layer at the interface to the organic layer stack
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
Organic electroluminescent device with a layer stack (1, 2, 3) for emitting light (4) through an at least partly transparent top electrode (3) comprising a conductive foil (1) comprising a carrier material (11) with an upper and a lower side as a substrate and a first metal layer (12) with a thickness resulting in a sheet resistance of less than 0.05 O/square on the upper side of the carrier material (11), the latter comprising at least a first metal layer (121) as a bottom electrode, an organic layer stack (2) deposited on top of the bottom-electrode (11) and designed to emit light (4), the transparent top electrode (3) on top of the organic layer stack (2), and at least partly transparent protection element (5) covering at least the top electrode and the organic layer stack (2).