Organic EL Device Segmented Emission Layers
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Solution Overview
Problem
Conventional organic EL devices face challenges in achieving practical luminous efficiency and emission lifetime due to the deactivation of triplet states in blue-emitting layers, with existing host materials either having inappropriate energy gaps or short lifetimes.
Innovation Solution
An organic EL device structure incorporating a fluorescent-emitting layer with a host and dopant, and red and green phosphorescent-emitting layers, where the green phosphorescent emission is primarily generated by charge recombination, allowing for the selection of materials with suitable singlet and triplet energy gaps, enhancing luminous efficiency and lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a blue fluorescent-emitting layer is used to generate triplet excitons for diffusion to red and green phosphorescent layers, then luminous efficiency is improved, but the host material must have a large triplet energy gap which conflicts with achieving practical emission lifetime
Solution Approach 1:
The device is divided into separate fluorescent-emitting layer and phosphorescent-emitting layers with distinct functions. The blue fluorescent layer generates excitons while the red and green phosphorescent layers receive triplet energy, allowing optimization of each layer independently for both efficiency and lifetime
Solution Approach 2:
Blocking layers are introduced as intermediaries between the blue fluorescent layer and red/green phosphorescent layers. These blocking layers facilitate controlled triplet energy transfer while protecting the phosphorescent layers from direct charge injection, thereby extending device lifetime without sacrificing luminous efficiency
2Loss of energy
If conventional host materials like CBP are used in the blue fluorescent-emitting layer to enable triplet diffusion, then energy transfer to phosphorescent layers is improved, but the singlet energy gap is too large for efficient energy transfer from dopant
Solution Approach 1:
The patent optimizes the energy gap parameters of the host material by selecting compounds with triplet energy gaps of 2.1-3.0 eV and singlet energy gaps of 3.5-4.5 eV. This parameter optimization enables efficient energy transfer at each stage: from dopant to host (singlet), and from host to phosphorescent layers (triplet), resolving the contradiction between energy transfer efficiency and luminous efficiency
3Productivity
If triplet energy is diffused from blue fluorescent layer to red and green phosphorescent layers, then utilization of triplet excitons is improved, but material selection is constrained by required energy gap relationships
Solution Approach 1:
By defining specific energy gap ranges (triplet: 2.1-3.0 eV, singlet: 3.5-4.5 eV), the patent creates a standardized parameter framework that enables systematic material selection. This approach maintains high triplet utilization efficiency while providing flexibility to choose from multiple compounds within these ranges, including carbazole derivatives and other suitable materials
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 enables efficient white emission by utilizing both singlet and triplet excitons, improving luminous efficiency and extending the device's emission lifetime while allowing for the use of materials with excellent heat resistance and charge stability.
Implementation Method 1
Emission from the singlet state is called as fluorescence
Implementation Method 2
Emission from the triplet state is called as phosphorescence
Implementation Method 3
the triplet in the blue fluorescent-emitting layers is diffused in the red and green phosphorescent-emitting layers via the blocking layers. Then, the triplet in the red and green phosphorescent-emitting layers is generated, from which red and green phosphorescence is obtainable
Implementation Method 4
the green phosphorescent dopant emitting light mainly by recombination of charges within the green phosphorescent-emitting layer
Implementation Method 5
the triplet in the blue fluorescent-emitting layers is diffused in the red and green phosphorescent-emitting layers via the blocking layers
Data Source
AI summary
An organic EL device includes: an anode (3); a cathode (4); and an organic thin-film layer (5) provided between the anode (3) and the cathode (4). The organic thin-film layer (5) includes: a fluorescent-emitting layer (51) containing a fluorescent host and a blue fluorescent dopant; a red phosphorescent-emitting layer (52) containing a red phosphorescent host and a red phosphorescent dopant; and a green phosphorescent-emitting layer (53) containing a green phosphorescent host and a green phosphorescent dopant. The red phosphorescent dopant emits light mainly by receiving transfer of triplet energy from the fluorescent host. The green phosphorescent dopant emits light mainly by recombination of charges within the green phosphorescent-emitting layer.