Organic EL Device White Light Stability via Triplet Energy Management
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Solution Overview
Problem
Existing organic electroluminescence (EL) devices face challenges in producing stable white light emission due to low blue light emission when luminescent materials for RGB are included in a single layer, as variations in evaporation rates cause color irregularities.
Innovation Solution
Incorporating a blue phosphorescent material with a luminescence peak between 420 nm and 500 nm, a green phosphorescent material with a peak between 500 nm and 570 nm, and a red phosphorescent material with a peak between 570 nm and 650 nm, along with a charge-transporting material having a lowest excited triplet energy level of 2.7 eV or more, which is higher than the blue phosphorescent material by 0.08 eV, to suppress exciton energy transfer and stabilize white light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If luminescent materials for RGB are included in a single luminescent layer, then the device structure is simplified, but color irregularities occur due to variations in evaporation rates
Solution Approach 1:
The invention divides the luminescent layer into three separate luminescent layers, each containing a specific phosphorescent material (blue, green, or red) and a charge-transporting material. This segmentation allows independent control of each color layer's thickness and composition, eliminating color irregularities caused by evaporation rate variations in a single-layer structure while maintaining overall device simplicity.
2Reliability
If a charge-transporting material with high T1 level is used, then exciton energy transfer is suppressed and white light emission is stabilized, but the material selection range is limited
Solution Approach 1:
The invention establishes a specific parameter criterion for charge-transporting materials: the lowest excited triplet energy level (T1) must be 2.7 eV or more, and must be higher than the blue phosphorescent material's T1 by 0.08 eV or more. This parameter-based approach provides clear selection guidelines that ensure exciton energy transfer suppression and stable white light emission, while still allowing flexibility in choosing from various materials that meet these energy level requirements.
3Manufacturing precision
If separate luminescent layers for RGB are formed, then color uniformity is improved, but the device structure and manufacturing process become more complex
Solution Approach 1:
The charge-transporting materials used in each luminescent layer serve multiple functions: they transport charges (holes or electrons) within their respective layers and simultaneously act as host materials for the phosphorescent dopants. This multi-functionality reduces the need for additional separate layers, thereby improving color uniformity through structured separation while limiting the increase in 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 enables the production of organic EL devices that emit white light with reduced color irregularities and increased stability by effectively managing exciton energy transfer, allowing for reliable adjustment of dope densities and improved luminance efficiency.
Implementation Method 1
the T1 of the charge-transporting material being higher than the T1 of the blue phosphorescent material by 0.08 eV or more to suppress exciton energy transfer
Implementation Method 2
a blue phosphorescent material having a luminescence peak in a range of from 420 nm to less than 500 nm, a green phosphorescent material having a luminescence peak in a range of from 500 nm to less than 570 nm, a red phosphorescent material having a luminescence peak in a range of from 570 nm to 650 nm
Implementation Method 3
When a voltage is applied between the electrodes, excitons are generated in the luminescent layer positioned between the electrodes, as a result of re-combination of holes and electrons, and excessive energy is emitted as light when the excitons return from the excited state to the ground state
Data Source
AI summary
The invention provides an organic EL device including a pair of electrodes and at least one luminescent layer located between the pair of electrodes, the luminescent layer including a blue phosphorescent material having a luminescence peak in a range of from 420 nm to less than 500 nm, a green phosphorescent material having a luminescence peak in a range of from 500 nm to less than 570 nm, a red phosphorescent material having a luminescence peak in a range of from 570 nm to 650 nm, and a charge-transporting material, the charge-transporting material having a lowest excited triplet energy level (T1) of 2.7 eV or more, and the T1 of the charge-transporting material being higher than the T1 of the blue phosphorescent material by 0.08 eV or more.