Organic EL Element LUMO Level and Film Thickness Optimization
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Solution Overview
Problem
Organic electroluminescence (EL) elements with existing optical resonator structures face challenges in reducing drive voltage and improving light emission efficiency and lifetime due to limitations in energy band structures and film thicknesses of functional layers.
Innovation Solution
An organic EL element design featuring a cathode-anode structure with a light-emitting layer sandwiched between an electron transport layer and an electron injection layer, where the LUMO level difference between the light-emitting and electron transport layers is at least 0.5 eV, and the electron injection layer's film thickness is greater than the electron transport layer's, forming a first-order or higher optical interference resonator structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If an optical resonator structure is implemented in an organic EL element, then light extraction efficiency is improved, but drive voltage reduction and lifetime improvement are limited
Solution Approach 1:
The patent changes the energy level parameters by ensuring the LUMO level of the electron transport layer is at least 0.5 eV lower than that of the light-emitting layer, and adjusts the film thickness parameter of the electron injection layer to be greater than that of the electron transport layer. These parameter changes enable first-order or higher optical interference while achieving reduced drive voltage and improved lifetime alongside enhanced light extraction efficiency.
2Reliability
If the LUMO level difference between light-emitting layer and electron transport layer is increased to at least 0.5 eV, then electron injection is optimized, but device complexity increases
Solution Approach 1:
The patent simplifies the energy band structure design by establishing a clear quantitative parameter: the LUMO level of the electron transport layer must be at least 0.5 eV lower than that of the light-emitting layer. This specific parameter change provides a straightforward design criterion that optimizes electron injection while avoiding excessive complexity in the energy band structure design.
3Illumination intensity
If film thickness of the electron injection layer is increased to be greater than the electron transport layer, then optical interference resonance is enhanced, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the film thickness parameter relationship by specifying that the electron injection layer thickness must be greater than the electron transport layer thickness. This parameter change enables first-order or higher optical interference resonance while providing a clear manufacturing guideline that balances optical performance with fabrication precision requirements.
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 reduces drive voltage, enhances light emission efficiency, and extends the lifetime of the organic EL element by optimizing electron injection and light extraction through a larger electron injection barrier and reduced influence of film thickness on operational properties.
Implementation Method 1
an optical resonator structure is provided between a face of the anode facing the cathode and a face of the cathode facing the anode. In other words, by aligning phases of light transmitted from the light-emitting layer through a light transmissive electrode and light reflected at least once at the face of the electrode, light emitted from the light-emitting layer is mutually strengthened so as to improve light extraction efficiency
Implementation Method 2
an electron injection layer disposed between the electron transport layer and the cathode, in contact with the electron transport layer, wherein a difference between lowest unoccupied molecular orbital (LUMO) level of the light-emitting layer and LUMO level of the electron transport layer is at least 0.5 eV, and film thickness of the electron injection layer is greater than film thickness of the electron transport layer
Implementation Method 3
An organic EL element has a structure in which at least a light-emitting layer is sandwiched between an anode and a cathode
Data Source
AI summary
An organic EL element includes an anode, a cathode opposing the anode, a light-emitting layer disposed between the anode and the cathode, an electron transport layer disposed in contact with a cathode-side surface of the light-emitting layer, and an electron injection layer disposed between the electron transport layer and the cathode, in contact with the electron transport layer. A difference between the lowest unoccupied molecular orbital (LUMO) level of the light-emitting layer and the LUMO level of the electron transport layer is at least 0.5 eV. The film thickness of the electron injection layer is greater than the film thickness of the electron transport layer.