Transparent Cathode Adjacent Layer for OLED Light Extraction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing organic electroluminescence elements face challenges in achieving high light extraction efficiency due to waveguide loss of surface plasmon mode light and variations in brightness with viewing angle, particularly when using thin metal cathodes and light scattering layers, which also impact driving voltage and lifetime.
Innovation Solution
An organic electroluminescence element with a transparent cathode of 2-10 nm thickness and an adjacent layer with a refractive index of 1.6-1.95, containing no light scattering particles, optimized to reduce waveguide loss and enhance luminous efficiency, along with specific metal complex compounds and electron transporting layers to improve performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the metal thin-film cathode is thinned to ensure sufficient electrical conductivity, then electrical conductivity is improved, but transmission of the cathode decreases and light extraction efficiency is reduced
Solution Approach 1:
An adjacent layer with refractive index 1.6-1.95 is introduced between the transparent cathode and the light emitting layer. This intermediary layer mediates the optical interaction, reducing waveguide loss of surface plasmon mode light while allowing the cathode to maintain thin thickness for both conductivity and transparency.
Solution Approach 2:
The refractive index of the adjacent layer is specifically controlled within 1.6-1.95, and its thickness is optimized at 15-180 nm. These parameter changes enable effective reduction of waveguide loss without compromising the electrical conductivity or transparency of the thin cathode.
2Loss of energy
If the metal thin-film cathode is thinned to improve transparency, then light extraction efficiency is improved, but electrical conductivity is damaged
Solution Approach 1:
The adjacent layer acts as an optical intermediary that enhances light extraction efficiency without requiring the cathode to be thicker. This allows the cathode to remain thin for transparency while the adjacent layer compensates for the reduced light extraction that would normally occur with thin metal films.
3Loss of energy
If a light scattering layer is provided to improve light extraction efficiency, then light extraction efficiency is improved, but transmission of the element decreases
Solution Approach 1:
The adjacent layer with refractive index 1.6-1.95 serves as an intermediary that reduces waveguide loss without the need for light scattering particles. This maintains high transmission of the element while improving light extraction efficiency, unlike light scattering layers that reduce transmission.
4Volume of moving object
If the distance between the light emitting layer and metal electrode is small, then the element structure is compact, but waveguide loss of surface plasmon mode light is large
Solution Approach 1:
The adjacent layer with refractive index 1.6-1.95 is positioned between the light emitting layer and the transparent cathode, acting as an intermediary that reduces waveguide loss of surface plasmon mode light. This allows the element to maintain a compact structure with small distance between layers while effectively reducing optical loss.
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 results in lower driving voltage and improved luminous efficiency with reduced waveguide loss and minimal brightness variation across viewing angles, enhancing overall performance of the organic electroluminescence element.
Implementation Method 1
Patent document 1 discusses a method to improve the light extraction efficiency by using optical interference
Implementation Method 2
the cathode is a transparent layer containing a metal and having a film thickness of 2 nm or more but less than 10 nm
Implementation Method 3
an organic electroluminescence element, which uses an organic material to emit light by electric energy from a positive electrode and a negative electrode
Data Source
AI summary
Provided are an organic electroluminescence element, an illumination device, and a display device having lower driving voltage and excellent luminous efficiency. An organic electroluminescence element has a supporting substrate; and a cathode, a light emitting layer and an adjacent layer provided on the supporting substrate, wherein the adjacent layer is arranged adjacent to the outer side of the cathode (i.e., the side opposite to the light emitting layer), wherein the cathode is a transparent layer containing a metal and having a film thickness of 2 nm or more but less than 10 nm; and wherein the adjacent layer has a refractive index of between 1.6 and 1.95, a film thickness of between 15 nm and 180 nm, and contains no light scattering particle.