Planar Light Emitting Device Brightness Uniformity
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Solution Overview
Problem
Planar light emitting devices with organic EL elements face issues of brightness uniformity and increased area of non-light emitting parts due to high sheet resistance of transparent anodes and limited area expansion, leading to disfigurement when multiple elements are arranged.
Innovation Solution
A planar light emitting device design featuring a transparent substrate with a quadrilateral organic EL element, including a transparent conductive film anode, organic light emitting layer, and metal cathode, with auxiliary electrodes and feeding parts to reduce potential gradients and contact resistance, and a sealing member with metal foil for improved humidity resistance and heat radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a transparent conductive film is used as a planar anode to achieve high brightness, then brightness is improved, but sheet resistance is high causing large electric potential gradient and large voltage application, resulting in large dispersion in brightness
Solution Approach 1:
The planar anode is segmented into multiple independent transparent conductive film regions (first, second, third, and fourth transparent conductive films) arranged in a grid pattern. This segmentation reduces the sheet resistance effect by providing multiple parallel current paths, thereby reducing electric potential gradient and improving brightness uniformity across the light emitting area.
2Manufacturing precision
If a non-luminous insulation layer is added to improve brightness uniformity, then brightness uniformity is improved, but the area of non-light emitting part increases, limiting area expansion of the light emitting part
Solution Approach 1:
The non-luminous insulation layer is extracted and positioned only in the non-light-emitting regions surrounding the light emitting area. The light emitting area itself remains free of this insulation layer, allowing maximum light emission while the insulation layer provides necessary electrical isolation and brightness uniformity control in the peripheral regions.
Solution Approach 2:
The non-luminous insulation layer is applied selectively with local quality - present in non-light-emitting regions for electrical isolation and brightness control, but absent from the light emitting area to maximize light output. This localized application optimizes both brightness uniformity and light emitting area.
3Reliability
If electrode terminals are located at opposite edges of the insulation substrate for electrical connection, then electrical connection is achieved, but distance between adjacent light emitting parts becomes large when multiple elements are arranged, causing disfigurement
Solution Approach 1:
The electrode terminals are arranged in a two-dimensional grid pattern on the same surface plane, rather than being positioned at opposite edges. This planar distribution allows multiple light emitting parts to be arranged compactly in both horizontal and vertical directions, reducing the distance between adjacent elements and improving overall arrangement compactness while maintaining reliable electrical connections.
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 design enhances brightness uniformity, reduces the area of non-light emitting parts, and increases luminance efficiency by minimizing potential gradients and contact resistance, while also improving heat radiation and preventing short circuits.
Implementation Method 1
a transparent conductive film can be used as a planar anode... the sheet resistance of the planar anode is higher than that of the planar cathode, and therefore an electric potential gradient becomes large in the planar anode
Implementation Method 2
an organic EL element (an organic electroluminescence device)... An organic EL layer containing organic light emitting material is then formed on the transparent electrode and the non-luminous insulation layer to coat them
Implementation Method 3
a metal membrane can be used as a planar cathode... the opposite electrode is connected to the power source through an electrode terminal located at another opposite edge of the insulation substrate with translucency
Implementation Method 4
The whole light emitting part is then airtight sealed with a seal member made of glass or stainless steel
Implementation Method 5
a non-luminous insulation layer arranged in a pattern is formed in a required region of a surface of the transparent electrode
Data Source
AI summary
Planar light emitting device includes: anode and cathode feeding parts formed on first surface side of transparent substrate and electrically connected to quadrilateral planar anode and cathode, respectively; quadrilateral frame shaped anode auxiliary electrode formed at the whole circumference of surface of the planar anode; anode feeding auxiliary electrode integrally and continuously formed to the auxiliary electrode and laminated on anode feeding part. Two distances between predetermined two parallel sides of four sides of a light emitting part and outer circumferential edges of the transparent substrate on sides adjacent to the two parallel sides, respectively are smaller than two distances between the other two parallel sides and the outer circumferential edges of the transparent substrate on sides adjacent to the other two parallel sides, respectively.