Organic EL Space Layer for Carrier Balance
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Solution Overview
Problem
The existing organic electroluminescence (EL) devices face challenges in achieving high luminous efficiency and color rendering properties due to difficulties in electron and hole injection and transportation through bipolar layers with high triplet energy, which leads to imbalance in carrier recombination and reduced efficiency.
Innovation Solution
Incorporating a space layer with specific compounds that satisfy certain energy and refractive index conditions, such as ΔST ≤ 0.5 eV, a half bandwidth of photoluminescence spectrum greater than 80 nm, and Δn > 0.04, to facilitate balanced carrier injection and transportation between phosphorescent and fluorescent emitting layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a bipolar layer containing a compound with large triplet energy is used to prevent Dexter transfer, then triplet energy transfer is inhibited, but electron and hole injection and transportation become difficult
Solution Approach 1:
The patent introduces a space layer as an intermediary component between the fluorescent-emitting layer and phosphorescent-emitting layer. This space layer contains a compound with specific energy characteristics (singlet energy EgS of 2.70-3.50 eV, triplet energy EgT of 2.40-3.20 eV, and ΔST ≤ 0.5 eV) that acts as a mediator to enable balanced carrier injection and transportation while preventing harmful triplet energy transfer to the fluorescent layer.
Solution Approach 2:
The patent applies parameter changes by carefully selecting compounds with specific energy parameters for the space layer. The key parameters include singlet energy (EgS), triplet energy (EgT), and their difference (ΔST), which are optimized to achieve the desired balance between carrier transport and triplet energy blocking. This precise parameter control allows the space layer to fulfill multiple functions simultaneously.
2Device complexity
If the fluorescent-emitting layer and phosphorescent-emitting layer are laminated adjacent to each other, then device structure is simplified, but carrier recombination balance deteriorates and triplet energy transfer occurs
Solution Approach 1:
The space layer serves as a necessary intermediary between the fluorescent and phosphorescent emitting layers. Although it adds a layer to the device structure, it enables efficient carrier recombination balance and prevents triplet energy transfer, thereby improving overall luminous efficiency. The space layer's specific energy parameters ensure it facilitates carrier transport while blocking harmful energy transfer.
3Loss of energy
If a compound with large singlet energy is used in the bipolar layer to block triplet energy, then triplet energy transfer is prevented, but injection and transportation of electrons and holes becomes difficult
Solution Approach 1:
The patent resolves this contradiction by changing the energy parameters of the space layer compound to specific ranges: singlet energy EgS of 2.70-3.50 eV, triplet energy EgT of 2.40-3.20 eV, and their difference ΔST ≤ 0.5 eV. These parameter changes enable the compound to have appropriate energy levels for facilitating carrier injection and transportation while maintaining the ability to block triplet energy transfer.
Solution Approach 2:
The space layer compound acts as an intermediary with specifically tuned energy levels that mediate between the requirements of carrier transport and triplet energy blocking. The small ΔST value indicates close proximity between singlet and triplet energy levels, which facilitates carrier injection while the absolute energy values ensure triplet energy blocking capability.
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 enhances luminous efficiency and color rendering properties by improving carrier balance and exciton transfer efficiency, resulting in improved performance of organic EL devices with balanced emission of blue, green, and red lights.
Implementation Method 1
injection and transportation of electrons and holes through the bipolar layer becomes difficult
Implementation Method 2
it has been known that the internal quantum efficiency can be improved up to 100% when intersystem crossing efficiently occurs from the singlet excitons
Implementation Method 3
The injected electrons and holes are recombined in an emitting layer to form excitons
Implementation Method 4
such a device arrangement enables to provide an organic EL device that inhibits Dexter transfer of triplet energy
Data Source
AI summary
An organic electroluminescence device includes a pair of electrodes and an organic compound layer interposed therebetween. The organic compound layer includes a plurality of emitting layers including a first emitting layer and a second emitting layer, in which at least one of the first and second emitting layers contains a phosphorescent dopant material, and a space layer between the first and second emitting layers. The space layer contains a compound satisfying a relationship of the following numerical formula (1) in terms of a difference ΔST between singlet energy EgS and an energy gap Eg77K at 77K,[Numerical Formula 1]ΔST=EgS−Eg77K≦0.5 (eV) (1).