Organic EL Element Nanometer Columnar Electrode Light Extraction
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Solution Overview
Problem
Conventional organic electroluminescence (EL) elements have low light extraction efficiency, typically ranging from 20% to 30%, necessitating improvements in both top-emission and bottom-emission types to enhance external quantum efficiency.
Innovation Solution
An organic EL element is designed with a substrate, a reflecting first electrode featuring nanometer-size columnar structures with a metallic surface, and a transparent second electrode, where the columnar structures have heights less than the organic EL layer thickness and pitches longer than their heights, optimized through a manufacturing process involving vacuum deposition and crystal growth methods to improve light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a flat reflecting electrode is used in conventional organic EL elements, then the device structure is simple and easy to manufacture, but the light extraction efficiency is low (20-30%) due to plasmon loss
Solution Approach 1:
The flat reflecting electrode is segmented into multiple columnar structures with periodic arrangement. This segmentation transforms the continuous metallic surface into discrete vertical columns, which reduces plasmon loss by preventing lateral electron oscillations while maintaining vertical reflection functionality. The segmented structure extracts light more efficiently by directing photons outward at multiple positions along the column heights.
Solution Approach 2:
The electrode structure transitions from a two-dimensional flat surface to a three-dimensional columnar array. By adding the vertical dimension with columnar protrusions, the electrode provides multiple light extraction interfaces at different heights and positions, increasing the solid angle for light emission and reducing reliance on single-plane extraction, thereby improving overall light extraction efficiency.
2Loss of energy
If columnar structures with metallic surfaces are formed on the substrate, then light extraction efficiency is improved, but the manufacturing process becomes more complex
Solution Approach 1:
Organic semiconductor material layers are deposited and annealed beforehand to form columnar cores before the metallic electrode material is deposited. This preliminary formation of organic columns provides a template that guides the subsequent metallic layer deposition, ensuring the metal automatically conforms to the columnar structure without requiring complex lithography or patterning steps for the metal itself.
Solution Approach 2:
The organic semiconductor material serves dual purposes: as the functional emission layer and as a self-organizing template for forming the columnar electrode structure. During vacuum deposition and annealing, the organic material spontaneously forms vertical columns through self-organization, which then automatically serve as the structural template for the metallic electrode, eliminating the need for separate patterning processes.
3Loss of energy
If the columnar structures have heights greater than the organic EL layer thickness, then light extraction may be enhanced, but short circuits between electrodes may occur
Solution Approach 1:
The columnar structures exhibit local quality differentiation where the upper portions extend into the organic EL layer for light extraction functionality, while the lower portions are embedded in the substrate for structural support and electrical grounding. The metallic coating is applied selectively to ensure continuity at the base while maintaining insulation where columns are spaced apart, achieving both light extraction and electrical reliability through spatially differentiated properties.
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 configuration significantly enhances light extraction efficiency by reducing plasmon loss and preventing short circuits, while maintaining electrical properties, resulting in improved in-plane brightness and emission intensity compared to conventional flat electrode designs.
Implementation Method 1
the first electrode is a reflecting electrode, and wherein the first electrode comprises a plurality of nanometer-size columnar structures formed on the one surface of the substrate, and each of the plurality of columnar structures has a metallic surface as the outermost surface
Implementation Method 2
heating, under inert gas atmosphere, a vapor-deposited film formed of the first organic semiconductor material at the one surface side of the substrate using a vacuum deposition method
Implementation Method 3
heating, under inert gas atmosphere, a vapor-deposited film formed of the first organic semiconductor material at the one surface side of the substrate using a vacuum deposition method, thereby dispersing the vapor-deposited film as a cluster
Implementation Method 4
forming of the columnar bodies is performed using a crystal growth method
Data Source
AI summary
An organic EL element comprises: a substrate; a first electrode formed at one surface side of the substrate; a second electrode opposing the first electrode; and an organic EL layer located between the first and second electrodes. In the organic EL element, the second electrode is a transparent electrode, and the first electrode is a reflecting electrode. The organic EL element is a top-emission type. The first electrode comprises a plurality of nanometer-size (nanometer-order) columnar structures formed on the above-mentioned one surface of the substrate, and each of the plurality of columnar structures has a metallic surface as the outermost surface.