Phosphorescent OLED Enhancement Layer for Short Excited-State Lifetime

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Solution Overview

Problem

Organic light emitting diodes (OLEDs) with phosphorescent emitters typically exhibit long excited state lifetimes, leading to device aging issues, as the duration of the exciton state correlates with the overall device aging rate.

Innovation Solution

Incorporating an enhancement layer with a plasmonic material that places the phosphorescent emissive layer within a threshold distance to enhance the Purcell effect, increasing the radiative decay rate and reducing the transient excited state lifetime to 200 ns or less, thereby stabilizing the emitter and extending the device's lifespan.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If phosphorescent emitters are used in OLEDs, then light emission efficiency is improved, but excited state lifetime becomes too long causing device aging

Engineering Contradiction:

Improvelight emission efficiencyVSAvoidexcited state lifetime

Core Design Contradiction:

Use of energy by moving objectVSDuration of action of stationary object

Solution Approach 1:

The patent modifies the optical environment parameters by introducing a plasmonic enhancement layer with specific materials (gold, silver, aluminum) and geometries (nanoparticles, nanorods, metamaterials) to change the radiative decay rate parameter, reducing excited state lifetime from microsecond to nanosecond scale while preserving phosphorescent emission efficiency

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a plasmonic enhancement layer as an intermediary component between the phosphorescent emissive layer and the environment, which mediates the radiative decay process by providing plasmonic modes that accelerate exciton decay without requiring changes to the phosphorescent emitter molecules themselves

Inventive Principle:

Principle #24Intermediary (Mediator)

2Illumination intensity

If phosphorescent emitters with long excited state lifetime are used, then light emission is achieved, but device stability deteriorates due to aging

Engineering Contradiction:

Improvelight emissionVSAvoiddevice stability

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The patent changes the radiative decay rate parameter by modifying the optical environment through plasmonic structures, reducing the excited state lifetime parameter from microsecond to nanosecond scale, which directly improves device stability while maintaining light emission capability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful effect of long-lived excitons (which cause device aging) into a beneficial effect by using plasmonic enhancement to accelerate their decay, transforming the problem of long excited state lifetime into a solution that maintains high emission efficiency while achieving short lifetime for improved stability

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 significantly increases the device's stability, with a 20-fold or more increase in lifetime (LT95) and improved performance at high brightness by reducing energy storage in the OLED, as demonstrated across various emission wavelengths.

Implementation Method 1

Methodology Applied

Scientific EffectPurcell effect:

Data Source

PatentUS12082428B2OLED with triplet emitter and excited state lifetime less than 200 ns

Publication Date: 2024.09.03 UNIVERSAL DISPLAY CORP

AI summary

Emissive devices are provided that include a phosphorescent emitter placed within a threshold distance of an enhancement layer to achieve transient lifetimes of 200 ns or less.