Light-Emitting Element Electrode Structure for High Efficiency
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Solution Overview
Problem
Current light-emitting elements face challenges in achieving high emission efficiency, low power consumption, and controlled emission color, particularly in the white EL+ color filter method, due to material instability and alignment accuracy issues in electrode structures, leading to corrosion, defects, and reduced light use efficiency.
Innovation Solution
A light-emitting element structure incorporating a conductive layer with a high reflectance function and an oxide layer containing In and a stabilizer (such as Al, Si, Ti, Ga, Y, Zr, Sn, La, Ce, Nd, or Hf) to prevent corrosion and improve electron injection properties, with a higher stabilizer content than In, and a microcavity structure for enhanced light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a material having high reflectance is used for one of the pair of electrodes to improve light extraction efficiency, then light extraction efficiency is improved, but it is difficult to select a stable material which also has high work function
Solution Approach 1:
The electrode is constructed as a composite structure with a reflective layer (such as aluminum or silver) stacked with an oxide layer (such as indium oxide, tin oxide, or zinc oxide). This composite structure combines the high reflectance of metals with the high work function and stability of oxides, simultaneously achieving improved light extraction efficiency and material stability.
Solution Approach 2:
By changing the physical and chemical parameters of the electrode materials—specifically selecting materials with appropriate combinations of reflectance and work function values, and optimizing their thickness ratios—the electrode achieves both high light extraction efficiency and stable electrical properties.
2Power
If a stacked structure of materials having high reflectance and high work function is used to achieve improvement of light extraction efficiency and reduction of drive voltage, then light extraction efficiency is improved and drive voltage is reduced, but electrons and oxygen might be donated and accepted at the interface between two stacked different kinds of materials resulting in corrosion of the electrode materials
Solution Approach 1:
The oxide layer serves as an intermediary between the reflective metal layer and the organic EL layer. It mediates the interface interactions by providing a stable, high-work-function surface that prevents direct contact between the metal and organic materials, thereby preventing electron and oxygen donation/acceptance reactions that would cause corrosion.
Solution Approach 2:
The oxide layer creates an inert chemical environment at the electrode-organic layer interface. Materials like indium oxide, tin oxide, and zinc oxide are chemically inert and resistant to oxidation, forming a stable interface that prevents corrosive reactions between the reflective metal layer and the organic EL materials.
3Loss of substance
If the white EL+ color filter method is used to share the EL layer among all subpixels, then loss of EL layer material is small and manufacturing cost is reduced, but light use efficiency decreases due to uncontrolled emission colors
Solution Approach 1:
The electrode structure with different oxide layers is applied locally to different subpixel regions. Each subpixel area has an electrode configuration optimized for its specific emission color requirements, allowing the common EL layer to emit different colors in different regions while maintaining high light use efficiency in each subpixel.
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 proposed structure enhances light extraction efficiency, reduces drive voltage, and allows for controlled emission colors, improving the productivity and resolution of display devices while minimizing material waste and manufacturing costs.
Implementation Method 1
the conductive layer has a function of reflecting light
Implementation Method 2
a method has been proposed, in which a micro optical resonator (microcavity) structure utilizing a resonant effect of light between a pair of electrodes is used to increase the intensity of light having a specific wavelength
Implementation Method 3
In a basic structure of such a light-emitting element, a layer containing a light-emitting substance (an EL layer) is interposed between a pair of electrodes. By applying a voltage between the pair of electrodes of this element, light emission from the light-emitting substance can be obtained.
Data Source
AI summary
An electrode layer having high reflectance and a light-emitting element having high emission efficiency are provided. The light-emitting element includes a first electrode layer, a second electrode layer, and an EL layer between the first electrode layer and the second electrode layer. The first electrode layer includes a conductive layer and an oxide layer in contact with the conductive layer. The conductive layer has a function of reflecting light. The oxide layer includes In and M (M represents Al, Si, Ti, Ga, Y, Zr, Sn, La, Ce, Nd, or Hf). A content of the M in the oxide layer is higher than or equal to a content of the In.