OLED Stack Structure With Matched HOMO Levels for Lower Hole Barriers

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional light-emitting elements face challenges with high hole-injection barriers between layers, particularly in blue light-emitting or phosphorescence-emitting elements, leading to reduced lifetime and emission efficiency, and the underlying material combinations are not well understood.

Innovation Solution

A novel stack structure is introduced with specific organic compounds and electron-accepting compounds, along with a light-emitting substance having a hole-trapping property, to equalize HOMO levels and reduce hole-injection barriers, while using bipolar materials for efficient carrier recombination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional heterostructure with stepped HOMO levels is used, then carrier recombination efficiency is improved, but hole-injection barrier between layers increases

Engineering Contradiction:

Improvecarrier recombination efficiencyVSAvoidhole-injection barrier

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies equipotentiality by designing the hole-transport layer and light-emitting layer to have substantially equal HOMO levels (within 0.2 eV), eliminating the stepped HOMO level structure. This creates an equipotential condition for hole injection, reducing the hole-injection barrier while maintaining efficient carrier recombination through the bipolar material design.

Inventive Principle:

Principle #12Equipotentiality

2Illumination intensity

If blue light-emitting or phosphorescence-emitting materials are used, then emission color is achieved, but hole-injection barrier increases and lifetime decreases

Engineering Contradiction:

Improveemission colorVSAvoidlifetime

Core Design Contradiction:

Illumination intensityVSDuration of action of stationary object

Solution Approach 1:

The patent applies parameter changes by carefully selecting and optimizing the HOMO level parameters of the organic compounds used in the hole-transport and light-emitting layers. By adjusting the HOMO levels to be substantially equal (within 0.2 eV), the patent reduces the hole-injection barrier for blue and phosphorescence-emitting materials, thereby extending element lifetime while maintaining the desired emission color.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If conventional layer structure is used, then manufacturing simplicity is maintained, but emission efficiency and lifetime are reduced

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidemission efficiency

Core Design Contradiction:

Ease of manufactureVSProductivity

Solution Approach 1:

The patent applies composite materials by using bipolar materials that possess both hole-transport and light-emitting properties within the same layer. This composite approach allows the hole-transport layer and light-emitting layer to have substantially equal HOMO levels, reducing hole-injection barriers and improving emission efficiency and lifetime while maintaining a relatively simple manufacturing process.

Inventive Principle:

Principle #40Composite materials

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 structure results in a light-emitting element with improved lifetime, emission efficiency, and reduced power consumption, minimizing drive voltage and preventing hole leakage to the cathode.

Implementation Method 1

In recent years, research and development have been extensively conducted on light-emitting elements using electroluminescence (EL). By voltage application to this element, the substance having a light-emitting property can emit light.

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 2

Light emission from a singlet excited state is called fluorescence

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Implementation Method 3

Light emission from a triplet excited state is called phosphorescence

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Data Source

PatentUS12484439B2Light-emitting element, light-emitting device, electronic device, and lighting device

Publication Date: 2025.11.25 SEMICON ENERGY LAB CO LTD

AI summary

Objects of the present invention are to provide: a light-emitting element having a long lifetime and good emission efficiency and drive voltage. One embodiment of the invention is a light-emitting element including, between an anode and a cathode, at least a stack structure in which a first layer, a second layer, and a light-emitting layer are provided in order from the anode side. The first layer includes a first organic compound and an electron-accepting compound. The second layer includes a second organic compound having a HOMO level differing from the HOMO level of the first organic compound by from −0.2 eV to +0.2 eV. The light-emitting layer includes a third organic compound having a HOMO level differing from the HOMO level of the second organic compound by from −0.2 eV to +0.2 eV and a light-emitting substance having a hole-trapping property with respect to the third organic compound.