Red Phosphorescent Compound for OLED Color Purity
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Solution Overview
Problem
Organic electroluminescent devices using red phosphorescent materials face challenges in achieving high color purity, luminescence efficiency, and long luminescence lifetime, as increased color purity leads to decreased relative spectral sensitivity, making it difficult to attain external quantum efficiency comparable to internal quantum efficiency.
Innovation Solution
A red phosphorescent compound represented by Formula 1 is used as a dopant in the light-emitting layer, which includes specific alkyl and alkoxy groups, and is combined with Al or Zn complexes and carbazole derivatives to enhance luminescence properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If red phosphorescent materials are used to increase color purity, then color purity is improved, but relative spectral sensitivity decreases
Solution Approach 1:
The patent modifies the chemical structure of phosphorescent compounds by introducing specific substituents (alkyl, alkoxy, aryl groups) at defined positions on the ligand framework. These structural parameter changes optimize the balance between color purity (CIE x-coordinate) and spectral sensitivity, achieving external quantum efficiency comparable to internal quantum efficiency while maintaining deep red emission.
Solution Approach 2:
The patent employs composite phosphorescent materials combining organic ligands with metal centers (Ir, Pt) to create phosphorescent complexes. This composite approach enables simultaneous achievement of high color purity and maintained spectral sensitivity through synergistic effects between the organic ligand structure and metal photophysics.
2Loss of energy
If phosphorescent materials are used to enhance luminescence efficiency, then internal quantum efficiency is improved, but external quantum efficiency remains limited due to spectral sensitivity loss
Solution Approach 1:
The patent systematically varies structural parameters of the phosphorescent ligands (electron-donating/withdrawing groups, steric bulk, conjugation length) to optimize the emission spectrum shape. This enables maintaining high internal quantum efficiency while improving spectral overlap with the human eye sensitivity curve, thereby enhancing external quantum efficiency.
3Illumination intensity
If red phosphorescent compounds are developed for high color purity, then CIE x-values increase, but luminescence lifetime and stability become challenging to maintain
Solution Approach 1:
The patent introduces specific functional groups at localized positions on the ligand structure (e.g., positions 4 and 4' on the bipyridine ring, or specific positions on phenanthroline) to achieve high color purity through localized electronic effects, while the overall molecular framework maintains structural stability and long luminescence lifetime.
Solution Approach 2:
The patent uses heavy metal centers (Ir, Pt) as intermediaries that facilitate radiative decay from triplet excited states, enabling high color purity emission while maintaining long luminescence lifetimes through spin-orbit coupling effects that mediate the phosphorescence process.
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
The red phosphorescent compound achieves high color purity, high luminescence efficiency, and long luminescence lifetime, with organic electroluminescent devices exhibiting operation voltages of 6.0 V or less, luminance of 800 cd/m2 or higher, and lifetimes of 3,500 hours or longer.
Implementation Method 1
red phosphorescent compound... for red phosphorescence emission... Both singlet excitons and triplet excitons are used in phosphorescence processes to exhibit higher luminescence efficiency
Data Source
AI summary
The invention relates to a red phosphorescent compound represented by the following Formula (1) and an organic electroluminescent (EL) device using the same:wherein