Top-Emission Organic EL Cathode Buffer Layer
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Solution Overview
Problem
Top-emission organic electroluminescence elements face issues with instability, reduced luminous efficiency, and shortened life due to damage from sputtering methods used for forming ITO films, as well as challenges in electron injection performance when alkali metals like barium contact ITO layers, leading to oxidation and performance deterioration.
Innovation Solution
Incorporating a cathode buffer layer made of hole-transporting organic materials, such as triarylamine derivatives or fullerenes, between the electron injection layer and the cathode, which are resistant to oxidation and enhance electron transport, along with an electron injection layer containing alkali metals, to stabilize the device and improve luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sputtering method is used to form ITO film for top-emission organic EL element, then transparent electrode with good conductivity is achieved, but damage to organic layers occurs and element life is shortened
Solution Approach 1:
The patent applies preliminary action by forming the organic luminescent layer and electron injection layer before forming the ITO transparent electrode. This sequence allows the organic layers to be protected from sputtering damage by completing their formation first, then adding the electrode layer on top. The cathode buffer layer is also formed preliminarily to prevent oxidation of the electron injection layer before it contacts the ITO layer.
Solution Approach 2:
The patent introduces a cathode buffer layer as an intermediary between the electron injection layer containing alkali metals and the ITO transparent electrode. This buffer layer made of hole-transporting organic material prevents direct contact between the reactive alkali metals and the ITO layer, thereby preventing oxidation of the electron injection layer while still allowing functional operation.
2Reliability
If alkali metals like barium are used in electron injection layer, then electron injection performance is improved, but oxidation occurs when contacting ITO layer leading to performance deterioration
Solution Approach 1:
The cathode buffer layer serves as an intermediary between the alkali metal-containing electron injection layer and the ITO transparent electrode. This buffer layer prevents direct oxidation of the alkali metals by the ITO layer while maintaining the electron injection function. The buffer layer is made of hole-transporting organic material that is resistant to oxidation.
Solution Approach 2:
The patent uses a composite structure combining the electron injection layer (with alkali metals for high electron injection performance) and the cathode buffer layer (with hole-transporting organic material for oxidation resistance). This composite approach allows both functionalities to coexist - the electron injection layer provides excellent electron injection while the buffer layer protects it from oxidation.
3Adaptability or versatility
If top-emission structure is used, then design flexibility and current compensation are improved, but organic layers are exposed to plasma damage during ITO formation
Solution Approach 1:
The patent applies preliminary action by completing the formation of all organic layers (hole injection layer, hole transport layer, organic luminescent layer, and electron injection layer) before forming the ITO transparent electrode through sputtering. This ensures the organic layers are already in place and can be protected from plasma damage by the subsequent electrode layer formation process.
Solution Approach 2:
The cathode buffer layer acts as an intermediary protective layer between the organic luminescent layer and the ITO transparent electrode. During the sputtering process, this buffer layer helps shield the underlying organic layers from plasma damage while still allowing the ITO layer to be properly formed.
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 provides a stable and efficient top-emission organic electroluminescence element with improved operational and storage life, reduced driving voltage, and enhanced luminous efficiency by protecting the electron injection layer and luminescent layer from damage and oxidation.
Implementation Method 1
an electron injection layer which is formed between the cathode and the organic luminescent layer, primarily contains at least one of an alkali metal and an alkali earth metal, and injects electrons into the organic luminescent layer
Implementation Method 2
An element is called an organic electroluminescence element (hereinafter referred to as an organic EL element) which includes a thin film of an organic material and two electrodes sandwiching the thin film and emits light in response to application of voltage (electroluminescence)
Implementation Method 3
the sputtering method or the method using plasma for forming an ITO film
Implementation Method 4
the sputtering method or the method using plasma for forming an ITO film
Data Source
AI summary
An organic electroluminescence element includes an anode and a transparent electrode cathode. An organic luminescent layer is located between the anode and the cathode. An electron injection layer is located between the cathode and the organic luminescent layer, and includes at least one of an alkali metal and an alkali earth metal to inject electrons into the organic luminescent layer. A cathode buffer layer is located between the electron injection layer and the cathode, and includes a hole-transporting organic material.