OLED Emissive Layer Structure for Low-Voltage Pixel Uniformity

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Solution Overview

Problem

In full-color organic light-emitting elements, sharing hole-transport or electron-transport layers among pixels leads to inconsistent element characteristics, resulting in increased driving voltage and reduced reliability due to suboptimal pixel structures.

Innovation Solution

A light-emitting element structure with multiple light-emitting layers, including phosphorescent and fluorescent materials, where the electron-transport layer has a lower triplet excitation energy level than the individual electron-transport materials, allowing for optimized element structure and shared functionality, reducing driving voltage and enhancing emission efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the hole-transport layer or electron-transport layer is shared by multiple pixels to reduce manufacturing steps, then productivity is improved, but element characteristics become inconsistent leading to increased driving voltage and reduced reliability

Engineering Contradiction:

ImproveproductivityVSAvoidreliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent divides the light-emitting element into multiple independent pixel regions, each with its own dedicated hole-transport layer and electron-transport layer. This segmentation allows each pixel to have optimized transport layers tailored to its specific light-emitting layer requirements, preventing characteristic inconsistency while maintaining manufacturing efficiency through simultaneous formation of multiple layers

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different electron-transport materials in different electron-transport layers according to the specific requirements of each light-emitting layer. For example, first electron-transport material is used in the first electron-transport layer, second electron-transport material in the second electron-transport layer, allowing each pixel region to have locally optimized transport properties matching its light-emitting characteristics

Inventive Principle:

Principle #3Local quality

2Reliability

If separate layers are provided for each pixel to optimize element characteristics, then reliability is improved, but the number of deposition steps increases reducing productivity

Engineering Contradiction:

Improveelement characteristics consistencyVSAvoidproductivity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent combines multiple electron-transport layers and hole-transport layers into a unified structure where first electron-transport layer, second electron-transport layer, first hole-transport layer, and second hole-transport layer are formed in an integrated manufacturing process. This merging approach allows separate optimized transport layers for each pixel while reducing the total number of deposition steps compared to completely separate layer formation

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent designs the electron-transport layers and hole-transport layers to serve multiple functions: they provide charge transport for their respective light-emitting layers, act as barrier layers, and enable simultaneous formation of multiple pixel structures. This multi-functionality allows a single set of deposition steps to create multiple optimized pixel regions with consistent characteristics

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 achieves low driving voltage and high emission efficiency while improving productivity by allowing the electron-transport layer to function across multiple light-emitting layers, optimizing each pixel's performance and reducing the number of deposition steps.

Implementation Method 1

a first phosphorescent material and a first electron-transport material; the second light-emitting layer includes a second phosphorescent material

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 2

the third light-emitting layer includes a fluorescent material

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Implementation Method 3

the first to third light-emitting elements are provided in contact with an electron-transport layer positioned on a cathode side

Methodology Applied

Scientific EffectElectron transport: Conduction (electrical)

Data Source

PatentUS12127471B2Light-emitting element, light-emitting device, electronic appliance, and lighting device

Publication Date: 2024.10.22 SEMICON ENERGY LAB CO LTD

AI summary

A light-emitting element which includes a plurality of light-emitting layers between a pair of electrodes and has low driving voltage and high emission efficiency is provided. A light-emitting element including first to third light-emitting layers between a cathode and an anode is provided. The first light-emitting layer includes a first phosphorescent material and a first electron-transport material; the second light-emitting layer includes a second phosphorescent material and a second electron-transport material; the third light-emitting layer includes a fluorescent material and a third electron-transport material; the first to third light-emitting elements are provided in contact with an electron-transport layer positioned on a cathode side; and a triplet excitation energy level of a material included in the electron-transport layer is lower than triplet excitation energy levels of the first electron-transport material and the second electron-transport material.