Top-Emission OLED Stack Structure for Electron Injection and Damage Prevention
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Solution Overview
Problem
Top-emission organic electroluminescent panels face challenges with inefficient electron injectability and damage to organic layers during the formation of transparent conductive films, leading to increased driving voltage and reduced luminous efficacy.
Innovation Solution
A stack structure comprising an electron transport layer, a first metal layer, a p-type oxide layer, and a transparent cathode, with an additional mixture layer of a p-type oxide and a hole transport material or a second metal layer between the electron transport layer and the transparent cathode, which enhances electron injectability and reduces damage to organic layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a transparent conductive film is used as the upper electrode to enable top emission, then light emission from the upper electrode side is achieved, but electron injection efficiency deteriorates due to large work function difference
Solution Approach 1:
An electron injection layer is introduced as an intermediary between the transparent conductive film (cathode) and the electron transport layer. This intermediate layer has a work function that bridges the gap between the cathode's large work function and the LUMO level of the organic material, enabling efficient electron injection while maintaining top emission structure
Solution Approach 2:
The work function parameter of the electrode interface is modified by introducing the electron injection layer with specifically selected materials having appropriate work function values. This parameter change resolves the energy level mismatch between the transparent cathode and organic electron transport layer
2Reliability
If a transparent conductive film is formed by sputtering or ion plating to improve transparency and conductivity, then film quality is enhanced, but organic layers are damaged by secondary electrons and plasma
Solution Approach 1:
The electron injection layer is formed as a protective preliminary layer before the transparent conductive film deposition. This pre-formed layer acts as a shield that prevents secondary electrons and plasma from damaging the underlying organic layers during the sputtering or ion plating process
Solution Approach 2:
The electron injection layer serves as a cushioning protective barrier that absorbs and mitigates the harmful effects of plasma and secondary electrons generated during transparent conductive film formation, protecting the organic layers from damage beforehand
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 improves luminous efficacy and decreases the driving voltage of top-emission organic electroluminescent panels, achieving performance comparable to bottom-emission structures while preventing damage during transparent cathode formation.
Implementation Method 1
The organic EL element emits light by recombining holes injected from an anode and electrons injected from a cathode in a light-emitting layer provided between the electrodes
Data Source
AI summary
The present invention provides an organic electroluminescent panel capable of increasing the luminous efficacy and decreasing the driving voltage of a top emission (TE) organic EL element. The organic electroluminescent panel of the present invention includes: a substrate; and an organic electroluminescent element provided on the substrate. The organic electroluminescent element is a top emission element that includes, in the order from the substrate side: an anode; a light-emitting layer; an electron transport layer; a first metal layer; a p-type oxide layer; and a transparent cathode. The top emission element is configured to emit light from the transparent cathode side. The light-emitting layer and the electron transport layer are each formed from an organic material. At least one of a mixture layer of a p-type oxide and a hole transport material and a second metal layer is provided between the electron transport layer and the transparent cathode.