Organic Light-Emitting Layer Structure for Efficient Phosphorescence
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Solution Overview
Problem
Conventional carrier-injection organic electroluminescence (EL) technologies suffer from low light emission efficiency due to the probabilistic preference for triplet excited states over singlet states, leading to energy loss as heat and inefficient use of organic light-emitting material, particularly when host molecules with poor hole-transport properties dominate, causing uneven light emission across the light-emitting layer.
Innovation Solution
Implementing an organic light-emitting layer structure with alternating n-type and p-type organic material layers, each containing an organic light-emitting material molecule, to facilitate direct recombination and energy transfer, thereby enhancing light emission efficiency by utilizing the organic light-emitting material's triplet excited state for phosphorescence, and optimizing the energy levels to prevent thermal deactivation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a host molecule with high electron-transport property is used, then electron transport is improved, but hole transport becomes poor causing uneven light emission
Solution Approach 1:
The patent applies local quality by creating distinct regions within the light-emitting layer: a first light-emitting region closer to the anode and a second light-emitting region closer to the cathode. Each region has optimized characteristics for its specific function, with the first region optimized for hole transport and the second region optimized for electron transport, thereby achieving uniform light emission across the entire layer while maintaining high electron-transport properties where needed.
2Illumination intensity
If organic light-emitting material concentration is increased to improve efficiency, then light emission intensity increases, but concentration quenching occurs reducing efficiency
Solution Approach 1:
The patent divides the light-emitting layer into two distinct light-emitting regions with different organic light-emitting material concentrations. The first light-emitting region has a higher concentration optimized for its emission characteristics, while the second light-emitting region has a lower concentration to avoid concentration quenching. This spatial differentiation allows each region to operate at its optimal concentration without suffering from the negative effects of high concentration in the entire layer.
3Loss of energy
If triplet excited state is utilized for light emission, then light emission efficiency improves, but thermal deactivation increases causing material deterioration
Solution Approach 1:
The patent utilizes phosphorescent organic light-emitting materials that can emit light from triplet excited states, changing the emission mechanism parameter to improve efficiency. By selecting materials with appropriate triplet energy levels and utilizing heavy metal effects to enable phosphorescence, the patent converts non-emissive triplet states into light-emitting states, thereby reducing thermal deactivation and improving overall light emission efficiency while maintaining material stability through proper material selection.
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 approach increases light emission efficiency by ensuring the organic light-emitting material is effectively excited and utilized across the layer, reducing thermal deactivation and improving quantum efficiency, while also preventing overcurrent and deterioration of materials.
Implementation Method 1
The organic light-emitting material molecule can transit to the ground state from the triplet excited state accompanied by light emission owing to spin-orbit interaction.
Implementation Method 2
a host molecule in the triplet excited state returns to the ground state by transferring the state to an organic light-emitting material molecule
Implementation Method 3
light emission can be obtained through the transition from the singlet excited state to the ground state
Data Source
AI summary
To provide a highly efficient organic light-emitting element. An extremely thin layer (a monomolecular film or the like) containing an organic light-emitting material such as an iridium complex is provided between a layer of an n-type organic material (an organic material having a high electron-transport property) and a layer of a p-type organic material (an organic material having a high hole-transport property). In a structure described above, in a layer of the organic light-emitting material, electrons are injected from the LUMO of the n-type organic material to the LUMO of the organic light-emitting material, and holes are injected from the HOMO of the p-type organic material to the HOMO of the organic light-emitting material, whereby the organic light-emitting material is brought into an excited state and emits light.