White OLED with High Triplet Energy Hole Transport Layer
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Solution Overview
Problem
Conventional white organic light emitting devices suffer from reduced luminous efficiency due to electrons or excitons generated in the light emitting layer being introduced into the hole transport layer, rather than being used for light emission, especially when the triplet energy level of the light emitting layer is similar to that of the hole transport layer.
Innovation Solution
A white organic light emitting device is designed with a hole transport layer or blocking layer having a triplet energy level higher than the adjacent light emitting layer, with a difference between triplet and singlet energy levels of 0.01 eV to 0.6 eV, preventing the introduction of electrons or excitons into the light emitting layer and enhancing external quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the triplet energy level of the hole transport layer is similar to that of the light emitting layer, then the device structure is simple, but electrons or excitons generated in the light emitting layer are introduced into the hole transport layer causing luminous efficiency deterioration
Solution Approach 1:
The patent changes the energy level parameter of the hole transport layer by selecting materials with triplet energy levels higher than the light emitting layer (e.g., TCTA with 2.8 eV, TAPC with 2.6 eV, or TAPB with 2.7 eV), thereby preventing exciton leakage while maintaining device structure simplicity
Solution Approach 2:
The patent introduces a blocking layer as an intermediary between the light emitting layer and hole transport layer. This blocking layer has a triplet energy level higher than the light emitting layer and a small singlet-triplet energy difference (0.01-0.6 eV), acting as an energy barrier to prevent exciton leakage into the hole transport layer
2Loss of energy
If a blocking layer is added to prevent exciton leakage, then luminous efficiency is improved, but device complexity increases
Solution Approach 1:
The blocking layer is designed with specific energy level parameters: triplet energy level higher than the light emitting layer and singlet-triplet energy difference of 0.01-0.6 eV. This precise parameter control enables effective exciton blocking while maintaining reasonable device complexity
Solution Approach 2:
The blocking layer is strategically positioned only at the interface between the light emitting layer and hole transport layer where exciton leakage occurs. This localized approach addresses the specific problem area without unnecessarily increasing overall device complexity
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 improves light emission efficiency by preventing the loss of triplet excitons or electrons, allowing them to be recombined and contribute to light emission, thereby enhancing the external quantum efficiency of the device.
Implementation Method 1
at least one of the first hole transport layer and the second hole transport layer has a triplet energy level higher than a triplet energy level of the light emitting layer adjacent thereto
Implementation Method 2
electrons or excitons generated in the light emitting layer are not used for light emission and are introduced into the hole transport layer
Implementation Method 3
a difference (ΔEst) between a triplet energy level and a singlet energy level of 0.01 eV to 0.6 eV
Implementation Method 4
allowing them to be recombined and contribute to light emission
Data Source
AI summary
The white organic light emitting device for improved efficiencies includes an anode and a cathode opposing each other on a substrate, a charge generation layer between the anode and the cathode, a first stack and a second stack interposed between the anode and the charge generation layer, and between the charge generation layer and the cathode, respectively, wherein at least one of a first hole transport layer and a second hole transport layer has a triplet energy level higher than a triplet energy level of the light emitting layer adjacent thereto, and a difference between a triplet energy level and a singlet energy level of 0.01 eV to 0.6 eV.