OLED Transition Layer for Light Extraction and Electron Injection
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Solution Overview
Problem
In OLED display technology, the cathode thickness is prone to being too thin, leading to island formation and defects, which results in reduced light transmittance and luminous efficiency, especially when the cathode is formed by co-evaporation of magnesium and silver or silver alone.
Innovation Solution
Incorporating a transition layer between the cathode and electron transport layer with specific refractive index and energy level matching, ensuring 0.05≤n1−n2≤0.4 and 0 eV≤|LUMO1−φ1≤2.6 eV, to facilitate electron injection and reduce reflection, thereby improving light extraction and luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cathode thickness is increased to avoid island formation and defects, then the reliability of the cathode structure is improved, but the light transmittance deteriorates leading to lower OLED luminous efficiency
Solution Approach 1:
The cathode structure is divided into multiple thin layers (first cathode layer with Mg:Ag=1:4 to 1:6, second cathode layer with pure Ag, thickness 5-15 nm) rather than using a single thick layer. This segmentation allows each layer to be optimized for different functions while maintaining overall structural stability and light transmittance
Solution Approach 2:
The cathode uses a composite structure combining magnesium and silver in specific ratios (Mg:Ag=1:4 to 1:6) in the first layer, followed by a pure silver second layer. This composite material approach leverages the advantages of both materials to achieve both structural reliability and optical performance
2Illumination intensity
If a transition layer with higher refractive index than electron transport layer is introduced, then the light extraction rate is improved by avoiding full reflection, but the device structure becomes more complex
Solution Approach 1:
A transition layer (TPD or mCP, thickness 0.5-5 nm) is introduced as an intermediary between the cathode and electron transport layer. This intermediate layer with refractive index 1.7-1.9 acts as an optical mediator to reduce reflection at the interface and improve light extraction efficiency
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 enhances light extraction rates and luminous efficiency by avoiding full reflection and reducing electron injection barriers, leading to improved performance in organic light-emitting display panels.
Implementation Method 1
A refractive index n1 of the transition layer for visible light with a wavelength of 500 nm and a refractive index n2 of the electron transport layer for the visible light with the wavelength of 500 nm satisfy that 0.05≤n1−n2≤0.4
Implementation Method 2
avoid full reflection of light emitted by the organic luminous layer when the light passes through the interface between the electron transport layer and the transition layer
Implementation Method 3
A lowest unoccupied orbital energy level LUMO1 of the transition layer and a work function φ1 of the cathode satisfy that 0 eV≤|LUMO1−φ1≤|≤2.6 eV
Implementation Method 4
A lowest unoccupied orbital energy level LUMO2 of the electron transport layer and the lowest unoccupied orbital energy level LUMO1 of the transition layer satisfy that 0.4 eV≤|LUMO1−LUMO2|≤1 eV
Implementation Method 5
On the luminous layer, electrons and holes combine to produce excitons. Excitons are unstable and release energy, the released energy is transferred to the molecules of organic light-emitting material in the luminous layer, causing the molecules of organic light-emitting material to transmit from the ground state to the excited state. The excited state is very unstable, the excited molecules return to the ground state from the excited state, and such radiative transition produces luminescence
Data Source
AI summary
Provided are an organic light-emitting display panel and an organic light-emitting display apparatus. The organic light-emitting display panel includes an array base substrate including a plurality of driving elements, and includes a plurality of organic light-emitting devices. Each of the plurality of organic light-emitting devices is corresponding to a respective one of the plurality of driving elements, and the each of the plurality of organic light-emitting devices includes an anode and a cathode, a cathode, an organic luminous layer, an electron transport layer, and a transition layer. The organic luminous layer is disposed between the anode and the cathode, the electron transport layer is disposed between the luminous layer and the cathode, and the transition layer is disposed between the cathode and the electron transport layer, and the transition layer includes an organic material.