OLED Hole Transport Layer Structure for Higher Luminous Efficiency

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Solution Overview

Problem

Existing organic electroluminescence display devices face challenges in achieving low driving voltage, high luminous efficiency, and long life, necessitating the development of materials and structures that can stabilize these characteristics.

Innovation Solution

A light emitting element with a multi-layered hole transport region comprising a first, second, and third hole transport layer, each containing amine compounds with specific refractive indices, and a display device incorporating these elements to enhance luminous efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single hole transport layer is used, then the device structure is simple, but the luminous efficiency is insufficient

Engineering Contradiction:

Improvehole transport structureVSAvoidluminous efficiency

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The hole transport region is divided into three distinct hole transport layers (first, second, and third hole transport layers) with different refractive indices. This segmentation allows each layer to contribute differently to light extraction, with the intermediate layer having a higher refractive index to enhance light scattering and extraction efficiency, thereby resolving the contradiction between structural simplicity and luminous efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each hole transport layer is assigned a specific refractive index characteristic: the first and third layers have lower refractive indices while the intermediate layer has a higher refractive index. This local differentiation in optical properties optimizes light extraction at different positions within the hole transport region, improving overall luminous efficiency without requiring complex device architecture.

Inventive Principle:

Principle #3Local quality

2Productivity

If multiple hole transport layers with different refractive indices are used, then the luminous efficiency is improved, but the device complexity increases

Engineering Contradiction:

Improveluminous efficiencyVSAvoidhole transport structure

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The hole transport region employs a composite structure consisting of three layers made from different amine compounds with distinct refractive indices. The first hole transport layer contains a first amine compound, the intermediate layer contains a second amine compound with higher refractive index, and the third layer contains a third amine compound. This composite material approach achieves enhanced light extraction through refractive index contrast while maintaining a relatively straightforward layered architecture.

Inventive Principle:

Principle #40Composite materials

3Productivity

If the refractive index difference between layers is large, then the light extraction efficiency is improved, but the manufacturing precision requirements increase

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoidlayer thickness control

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent specifies controlled refractive index differences between layers (difference between second and first refractive index is 0.1 to 1.1, and difference between second and third refractive index is 0.1 to 1.1) rather than extreme differences. This parameter optimization achieves effective light extraction while avoiding excessive manufacturing complexity. The refractive index values are selected within specific ranges to balance optical performance with manufacturability.

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 multi-layered hole transport structure improves luminous efficiency and potentially extends the life of the display device by optimizing the recombination of holes and electrons, thereby enhancing display performance.

Implementation Method 1

a first hole transport layer disposed adjacent to the first electrode and including a first amine compound having a first refractive index, a second hole transport layer disposed between the first hole transport layer and the emission layer, and including a second amine compound having a second refractive index greater than the first refractive index

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS12577195B2Light emitting element and display device including the same

Publication Date: 2026.03.17 SAMSUNG DISPLAY CO LTD

AI summary

A light emitting element includes a first electrode, a hole transport region disposed on the first electrode, an emission layer disposed on the hole transport region, an electron transport region disposed on the emission layer, and a second electrode disposed on the electron transport region, wherein the hole transport region includes a first hole transport layer disposed adjacent to the first electrode and including a first amine compound having a first refractive index, a second hole transport layer disposed between the first hole transport layer and the emission layer, and including a second amine compound having a second refractive index greater than the first refractive index, and a third hole transport layer disposed between the second hole transport layer and the emission layer, and including a third amine compound having a third refractive index less than the second refractive index, thereby having high luminous efficiency.