Elongated Bus for Current Spreading in Large Area OLEDs
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Solution Overview
Problem
Large area, planar flexible OLED devices face issues with current spreading due to high sheet resistance in transparent nonmetallic conductive materials like indium tin oxide, leading to non-uniform brightness and luminance across the device.
Innovation Solution
Incorporating an elongated bus on the peripheral region of the transparent conductive electrode layer, which is ductile and flexible, to enhance current spreading and maintain even luminance across the luminous region, with the bus material matched in electronic properties to the transparent conductive material and having a work function within 30% of the electron affinity of the indium tin oxide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If transparent nonmetallic conductive materials like indium tin oxide are used for the anode layer, then light transmissivity is improved, but sheet resistance increases leading to non-uniform current spreading
Solution Approach 1:
The patent combines transparent nonmetallic conductive material (indium tin oxide) with a metallic conductive material (silver, aluminum, or copper) to form a composite electrode structure. The metallic material is deposited in a discontinuous pattern as elongated structures along the periphery, creating a hybrid system that leverages the high transmissivity of the nonmetallic material while utilizing the low resistance of the metallic material for current spreading.
Solution Approach 2:
The metallic conductive material is deposited in a discontinuous pattern rather than as a continuous layer. The elongated structures are separated by spacing, allowing light to pass through the gaps while still providing effective current spreading pathways along the periphery of the OLED device.
2Productivity
If the device area is increased to create large area OLED panels, then productivity and output are improved, but brightness uniformity deteriorates due to insufficient current spreading
Solution Approach 1:
The patent addresses the two-dimensional current spreading problem in large area devices by introducing elongated metallic structures along the periphery in a specific spatial arrangement. These peripheral structures act as current distribution hubs that feed current into the interior regions, effectively managing current flow across large areas without compromising brightness uniformity.
3Illumination intensity
If the transparent conductive electrode layer is made more transparent, then light emission is improved, but electrical conductivity decreases leading to higher sheet resistance
Solution Approach 1:
The patent merges the transparent nonmetallic conductive material layer with discontinuous metallic conductive structures to create a hybrid electrode system. This combination allows the device to maintain high light transmissivity from the nonmetallic material while reducing resistive losses through the low-resistance metallic pathways that facilitate efficient current spreading.
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 elongated bus design effectively reduces resistive losses and achieves uniform luminance, enhancing the aesthetic appearance and longevity of large area OLED panels by minimizing luminance degradation over time.
Implementation Method 1
an elongated bus disposed on at least a portion of the peripheral region and adjacent to the first electrode layer, wherein the elongated bus is configured to spread current across a length dimension of the first electrode layer
Implementation Method 2
Light is emitted when current is applied across the cathode and anode. As a result of the electric current, electrons are injected into the organic layer from the cathode and holes may be injected into the organic layer from the anode. Electrons and holes generally travel through the organic layer until they recombine at a luminescent center
Data Source
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AI summary
Disclosed herein is a light emitting electrical package having a first electrode layer comprising a substantially transparent nonmetallic conductive material, and a plurality of light emitting elements disposed on said first electrode layer. The first electrode layer comprises a peripheral region, and an elongated bus is disposed on at least a portion of the peripheral region and adjacent the first electrode layer. The elongated bus is configured to spread current across a length dimension of said first electrode layer. Also disclosed are elongated bus structure designed intended to reduce the resistive losses along a transparent nonmetallic conductive contact at its edge or periphery. One design for an elongated bus comprises: (1) a conductive adhesive/metal foil/conductive adhesive sandwich structure; (2) another design comprises a vapor deposited bus of one or more materials; and a further design employs (1) and (2) in tandem.