Organic Electroluminescence Element Nanoparticle Cathode Plasmon Loss
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Solution Overview
Problem
In organic electroluminescence elements, the use of metal cathodes with high conductivity leads to surface plasmons, resulting in light loss and reduced extraction efficiency, and the formation of uneven structures to mitigate this can cause short circuits and reliability issues.
Innovation Solution
A metal layer with a nanosize uneven structure formed by a nanoparticle arrangement is used, where the nanoparticles are arranged in a planar fashion, creating a flatter interface between the organic layers, thereby suppressing surface plasmons and reducing the likelihood of short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal materials with high conductivity are used for the cathode layer, then electrical conductivity is improved, but surface plasmons occur causing light loss and reduced light extraction efficiency
Solution Approach 1:
An organic electron transporting layer is introduced as an intermediary between the metal cathode and the light-emitting layer. This layer has lower conductivity than the metal, suppressing surface plasmon generation, while still enabling sufficient electron transport. The intermediary layer converts the harmful high-conductivity metal surface into a controlled interface that prevents energy loss.
Solution Approach 2:
The electrical conductivity parameter of the cathode interface is changed by replacing the pure metal surface with an organic layer having different conductivity characteristics. This parameter change suppresses the plasmon effect while maintaining functional electron transport, resolving the contradiction between conductivity and light extraction efficiency.
2Loss of energy
If an uneven corrugated structure is formed on all layer interfaces to suppress surface plasmons, then light extraction efficiency is improved, but film thickness becomes non-uniform causing short circuits and reduced reliability
Solution Approach 1:
The uneven structure is localized only to the cathode layer interface where surface plasmons are generated, rather than being applied to all layer interfaces. This local application suppresses plasmons at the metal interface without creating short circuit risks in other layers, maintaining both light extraction efficiency and device reliability.
Solution Approach 2:
The solution segments the problem by applying the uneven structure only where needed (at the metal cathode interface) rather than uniformly across all interfaces. This segmentation allows plasmon suppression at the critical interface while avoiding the harmful effects of non-uniformity in other layers.
3Loss of energy
If an uneven structure is formed on the cathode layer surface to convert surface plasmons to light, then light extraction efficiency is improved, but the uneven structure increases the risk of short circuits
Solution Approach 1:
The cathode structure is made composite by combining the metal layer with an organic electron transporting layer. The metal provides conductivity, the uneven structure provides plasmon conversion, and the organic layer provides insulation and uniform interfaces, collectively resolving the contradiction between light extraction and short circuit prevention.
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
This configuration enhances light extraction efficiency while maintaining high reliability by converting surface plasmons into transmitted light and ensuring flat interfaces between organic layers, preventing short circuits.
Implementation Method 1
a state called a plasmon occurs in which free electrons in the metal oscillate collectively and act as pseudo-particles. That is to say, if light with a predetermined wavelength strikes the surface of the metal material, waves of coarse and fine patterns of an electron density, that is, surface plasmons occurs
Data Source
AI summary
Provided is a highly-reliable organic electroluminescence element in which loss of light due to surface plasmons generated on a metal surface is suppressed, the efficiency of light extraction to outside the element, and short circuits are unlikely to occur. The organic electroluminescence element includes a metal layer (1), on a surface of which a nanosize uneven structure is provided by a nanoparticle arrangement structure (6) in which nanoparticles (6a) are arranged in a planar fashion, and an organic layer (3) disposed on the uneven surface of the metal layer (1) and constituted by a plurality of layers including a light-emitting layer (31). Each interface between the plurality of layers of the organic layer (3) is flatter than the uneven surface of the metal layer (1).