OLED Intermediate Layer HOMO Optimization for Hole Injection

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Solution Overview

Problem

Existing organic light-emitting devices (OLEDs) face challenges in achieving low driving voltage, high efficiency, high brightness, and long lifespan.

Innovation Solution

An OLED structure that includes an iridium-free organometallic compound as a dopant in the emission layer, with specific conditions for the highest occupied molecular orbital (HOMO) energy levels to enhance luminescent efficiency and lifespan.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If conventional OLED structures are used, then basic light emission is achieved, but driving voltage is high and efficiency is low

Engineering Contradiction:

Improvedriving voltageVSAvoidefficiency

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent optimizes the HOMO energy level difference between the intermediate layer and emission layer to be 0.1-0.5 eV, which facilitates hole injection and reduces driving voltage while maintaining high efficiency. This specific parameter optimization resolves the contradiction between low driving voltage and high efficiency

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

An intermediate layer is introduced between the hole transport region and emission layer to mediate charge transfer. This intermediate layer with optimized HOMO level acts as a bridge to facilitate hole injection into the emission layer, simultaneously achieving low driving voltage and high luminescent efficiency

Inventive Principle:

Principle #24Intermediary (Mediator)

2Illumination intensity

If emission layers with high brightness are used, then light output is improved, but lifespan is reduced due to degradation

Engineering Contradiction:

ImprovebrightnessVSAvoidlifespan

Core Design Contradiction:

Illumination intensityVSDuration of action of stationary object

Solution Approach 1:

The patent employs an iridium-free organometallic compound as dopant in the emission layer, replacing expensive and potentially less stable iridium-based materials. This substitution maintains high luminescent efficiency and brightness while improving device stability and lifespan through the use of more stable alternative materials

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The intermediate layer creates a protective environment at the interface with the emission layer, reducing interfacial degradation and stabilizing the emission layer. This protective interface extends device lifespan while maintaining high brightness output

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

3Productivity

If standard hole transport materials are used, then hole transport is achieved, but hole injection into emission layer is insufficient

Engineering Contradiction:

Improvehole transportVSAvoidhole injection efficiency

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The intermediate layer serves as a mediator between the hole transport region and emission layer, facilitating efficient hole injection. By optimizing its HOMO energy level to be 0.1-0.5 eV higher than the emission layer, it creates an energy gradient that drives hole injection while maintaining overall hole transport capability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent specifically optimizes the HOMO energy level parameter of the intermediate layer relative to the emission layer (0.1-0.5 eV difference), which dramatically improves hole injection efficiency while maintaining adequate hole transport through the device

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 proposed OLED structure achieves high luminescent efficiency and a long lifespan by facilitating hole injection, reducing interfacial degradation, and maintaining high external quantum efficiency.

Implementation Method 1

the organic light-emitting device satisfies a condition of HOMO(h1) - HOMO(host) > 0 eV

Methodology Applied

Scientific EffectEnergy level gradient:

Implementation Method 2

The holes and the electrons recombine in the emission layer to produce excitons. These excitons transit from an excited state to a ground state, thereby generating light

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentEP3425690B1Organic light-emitting device

Publication Date: 2025.06.11 SAMSUNG ELECTRONICS CO LTD

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AI summary

An organic light-emitting device including a first electrode, a second electrode facing the first electrode, and an organic layer disposed between the first electrode and the second electrode, wherein the organic layer includes an emission layer and an intermediate layer disposed between the first electrode and the emission layer, wherein the intermediate layer directly contacts the emission layer, and wherein the intermediate layer includes a first hole transport material, wherein the emission layer includes a host and a dopant, wherein the dopant is an organometallic compound, provided that the dopant does not comprise iridium, and wherein the organic light-emitting device satisfies certain parameters described in the specification.