Hybrid Fluorescent Phosphorescent OLED Emissive Layer

Solution Overview

Problem

White OLEDs using only phosphorescent emissive materials have limited operational stability due to the lifetime of blue phosphorescent components, while those using only fluorescent materials have lower external quantum efficiency, necessitating a balance between efficiency and stability.

Innovation Solution

Organic light emitting devices are designed with a combination of fluorescent and phosphorescent emissive materials, where fluorescent emitters harness singlet excitons and phosphorescent emitters utilize triplet excitons, potentially achieving 100% internal quantum efficiency by separating and simultaneously emitting from both types of excitonic centers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If only phosphorescent emissive materials are used in white OLEDs, then external quantum efficiency is improved, but operational stability deteriorates due to the lifetime of blue phosphorescent components

Engineering Contradiction:

Improveexternal quantum efficiencyVSAvoidoperational stability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The emissive layer is segmented into distinct fluorescent and phosphorescent sub-layers. The fluorescent layer handles singlet excitons while the phosphorescent layer handles triplet excitons. This segmentation allows each material type to operate in its optimal performance regime, with fluorescent materials providing stability and phosphorescent materials providing high efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention merges fluorescent and phosphorescent emissive materials into a single hybrid device structure. By combining both material types in the emissive region, the device simultaneously achieves the operational stability of fluorescent materials and the high external quantum efficiency of phosphorescent materials, resolving the trade-off between these two parameters.

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If only fluorescent emissive materials are used in white OLEDs, then operational stability is improved, but external quantum efficiency deteriorates

Engineering Contradiction:

Improveoperational stabilityVSAvoidexternal quantum efficiency

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The emissive layer is segmented into distinct fluorescent and phosphorescent sub-layers. The fluorescent layer handles singlet excitons while the phosphorescent layer handles triplet excitons. This segmentation allows each material type to operate in its optimal performance regime, with fluorescent materials providing stability and phosphorescent materials providing high efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention merges fluorescent and phosphorescent emissive materials into a single hybrid device structure. By combining both material types in the emissive region, the device simultaneously achieves the operational stability of fluorescent materials and the high external quantum efficiency of phosphorescent materials, resolving the trade-off between these two parameters.

Inventive Principle:

Principle #5Merging (Combining)

3Use of energy by moving object

If a combination of fluorescent and phosphorescent emissive materials is used, then external quantum efficiency is improved, but device complexity increases

Engineering Contradiction:

Improveexternal quantum efficiencyVSAvoidemissive layer structure

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The emissive layer is segmented into distinct fluorescent and phosphorescent sub-layers. The fluorescent layer handles singlet excitons while the phosphorescent layer handles triplet excitons. This segmentation allows each material type to operate in its optimal performance regime, with fluorescent materials providing stability and phosphorescent materials providing high efficiency.

Inventive Principle:

Principle #1Segmentation

4Use of energy by moving object

If phosphorescent emissive materials are used, then internal quantum efficiency is improved, but color stability deteriorates over time due to blue phosphorescent component lifetime

Engineering Contradiction:

Improveinternal quantum efficiencyVSAvoidcolor balance stability

Core Design Contradiction:

Use of energy by moving objectVSStability of the object's composition

Solution Approach 1:

The emissive layer is segmented into distinct fluorescent and phosphorescent sub-layers. The fluorescent layer handles singlet excitons while the phosphorescent layer handles triplet excitons. This segmentation allows each material type to operate in its optimal performance regime, with fluorescent materials providing stability and phosphorescent materials providing high efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the emissive layer are assigned different material qualities: the fluorescent layer uses materials with long operational lifetimes and stable color properties, while the phosphorescent layer uses materials optimized for high internal quantum efficiency. This local differentiation of material properties allows the device to achieve both high efficiency and long-term color stability.

Inventive Principle:

Principle #3Local quality

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 the stability and efficiency of white OLEDs by achieving high external quantum efficiency and maintaining stable color balance as the drive voltage increases, with improved operational stability and luminance.

Implementation Method 1

high efficiency fluorescent emitters for harvesting the singlet fraction of the generated excitons

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Implementation Method 2

high efficiency phosphorescent emitters for the triplet fraction of the generated excitons

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Data Source

PatentUS7474048B2Fluorescent filtered electrophosphorescence

Publication Date: 2009.01.06 THE TRUSTEES OF PRINCETON UNIV

AI summary

The present invention relates to organic light emitting devices (OLEDs), and more specifically to OLEDS that emit light using a combination of fluorescent emitters and phosphorescent emitters for the efficient utilization of all of the electrically generated excitons.