Anode Structure for Organic EL Display Light Reflectance
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Solution Overview
Problem
Existing organic electroluminescence type display apparatus face challenges in achieving high luminous efficiency and bright display images due to issues with anode materials, such as low light reflectance, high specific resistance, and poor hole injection efficiency, particularly in top emission types, where materials like Ag and Al alloys suffer from surface oxidation and oxide reaction layers forming insulating interfaces.
Innovation Solution
An anode structure comprising an Al alloy film with Group 8 3d transition metals and oxygen, combined with an amorphous ITO film, is used to enhance light reflectance and hole injection efficiency, preventing oxide reaction layer formation and reducing contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If Ag or Al alloy film is used as anode material to achieve high light reflectance, then light reflectance is improved, but oxide reaction layers form creating insulating interfaces that reduce hole injection efficiency
Solution Approach 1:
A TiO2 intermediate layer is introduced between the Al alloy anode and the organic EL layer. This TiO2 layer serves as a mediator that prevents oxide reaction layer formation at the Al-organic interface while maintaining good hole injection properties. The TiO2 layer has appropriate work function and forms stable interfaces, resolving the contradiction between high reflectance and hole injection efficiency.
Solution Approach 2:
The anode structure uses a composite of Al alloy (for high reflectance) combined with TiO2 (for interface stability and hole injection). This composite structure leverages the advantages of both materials: Al alloy provides the required light reflectance while TiO2 ensures reliable hole injection by preventing detrimental oxide reactions.
2Reliability
If Cr or Mo is used as anode material to achieve high work function for efficient hole injection, then hole injection efficiency is improved, but light reflectance becomes low causing large loss of reflected light
Solution Approach 1:
The anode uses a composite structure where Al alloy (high reflectance) is combined with TiO2 (appropriate work function). This composite achieves both high light reflectance (Al alloy property) and sufficient hole injection efficiency (TiO2 property), avoiding the need to choose between Cr/Mo (good hole injection but poor reflectance) and pure Al/Ag (good reflectance but poor hole injection).
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 efficiency and prevents dark spots, achieving a bright display image by maintaining high light reflectance and efficient hole injection while suppressing the reduction of transparent conductive films.
Implementation Method 1
the anode is made of a metal material having light reflectivity. Accordingly, when the light generated in the organic EL layer is allowed to be transmitted through the cathode and is emitted to the upper portion of the substrate, the reflected light that is reflected on the anode made of the metal material can be emitted to the upper portion of the substrate at the same time
Implementation Method 2
as a result, there is a problem in that the efficiency of hole injection into the organic EL layer remarkably deteriorates. In the case of the Al film, there is another problem in that surface irregularities such as hillock are more likely to occur
Data Source
AI summary
An organic electroluminescence type display apparatus according to an aspect of the present invention includes: a thin film transistor formed on an insulating substrate; and an organic EL device connected to the thin film transistor and including at least an anode, an electroluminescence layer, and a cathode stacked on each other in this order. The anode includes: an Al alloy film having conductivity and including at least one kind of Group 8 3d transition metals, and oxygen, the at least one kind of the Group 8 3d transition metals and the oxygen being added to aluminum; and an amorphous ITO film formed on the Al alloy film.