OLED Emissive Layer Energy Transfer for Blue Stability

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Solution Overview

Problem

There is a deficit of efficient phosphorescent emissive materials that demonstrate long operational stability, particularly in the blue region, and fluorescent OLEDs face issues with high efficiency and stability under high current densities.

Innovation Solution

A light emitting device is designed with an emissive layer containing both phosphorescent and fluorescent emitters, where the phosphorescent emitter harvests electrogenerated excitons and transfers energy to the fluorescent emitter, primarily redistributing excited states to stable fluorescent emitters, enhancing operational stability while maintaining high efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If phosphorescent emitters are used to achieve high efficiency through triplet state emission, then the external quantum efficiency can reach near 100%, but the operational stability is poor particularly in the blue region

Engineering Contradiction:

Improveexternal quantum efficiencyVSAvoidoperational stability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent combines phosphorescent and fluorescent emitters in a single emissive layer to merge the high efficiency advantage of phosphorescent materials with the operational stability advantage of fluorescent materials. The phosphorescent emitter (e.g., Ir(ppy)3) harvests triplet excitons efficiently while the fluorescent emitter (e.g., Alq3) provides stable emission, achieving both near-100% external quantum efficiency and improved operational stability through synergistic interaction between the two emitter types.

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If fluorescent emitters are used to achieve long operational stability, then the device lifetime is extended, but the efficiency is limited due to loss of triplet excitons

Engineering Contradiction:

Improveoperational stabilityVSAvoidexternal quantum efficiency

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent introduces phosphorescent emitters as intermediaries that facilitate energy transfer from triplet excitons to fluorescent emitters. The phosphorescent emitter acts as a mediator that captures triplet excitons through spin-orbit coupling and transfers energy to the fluorescent emitter, enabling the fluorescent system to utilize triplet excitons that would otherwise be lost, thereby achieving near-100% external quantum efficiency while maintaining the operational stability of fluorescent materials.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Illumination intensity

If high current densities are applied to increase brightness, then the luminance is improved, but triplet-triplet annihilation occurs reducing efficiency and stability

Engineering Contradiction:

ImproveluminanceVSAvoidefficiency and stability under high current

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The patent changes the emitter composition parameters by incorporating both phosphorescent and fluorescent emitters in specific ratios within the emissive layer. This parameter change modifies the exciton utilization mechanism, allowing the system to maintain high efficiency and stability under high current densities by reducing triplet-triplet annihilation through the complementary emission mechanisms of the dual-emitter system.

Inventive Principle:

Principle #35Parameter changes

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 device achieves high device operational stability and efficiency by utilizing energy transfer mechanisms like FRET, ensuring efficient utilization of excitons and avoiding triplet-triplet annihilation, thereby improving color quality and stability.

Implementation Method 1

the phosphorescent emitter harvests electrogenerated excitons and transfers energy to the fluorescent emitter

Methodology Applied

Scientific EffectEnergy transfer:

Implementation Method 2

utilizing energy transfer mechanisms like FRET

Methodology Applied

Scientific EffectFRET:

Implementation Method 3

emission from the triplet state can be facilitated through spin orbit coupling which incorporates a heavy metal atom in order to perturb the triplet state and add in some singlet character to and achieve a higher probability of radiative relaxation

Methodology Applied

Scientific EffectSpin orbit coupling:

Implementation Method 4

emission from the triplet state, called phosphorescence, is very slow and the transition probability is very low

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 5

emission from the singlet state, called fluorescence, can be very rapid and consequently very efficient

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Data Source

PatentUS12492336B2Organic light-emitting diodes with fluorescent and phosphorescent emitters

Publication Date: 2025.12.09 THE ARIZONA BOARD OF REGENTS ON BEHALF OF THE UNIV OF ARIZONA

AI summary

A light emitting device includes a first electrode, a hole transporting layer in contact with the first electrode, a second electrode, an electron transporting layer in contact with the second electrode; and an emissive layer between the hole transporting layer and the electron transporting layer. The emissive layer includes a phosphorescent emitter, a fluorescent emitter, and a host, and the phosphorescent emitter harvests electrogenerated excitons and transfers energy to the fluorescent emitter.