Organic EL Light-Emitting Layer Concentration Gradient

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Solution Overview

Problem

Organic electroluminescence elements face challenges in achieving high light-emission efficiency and durability, particularly due to issues with carrier injection and transport, leading to reduced external quantum efficiency and increased driving voltage, as well as localized light emission that does not effectively utilize the entire light-emitting layer.

Innovation Solution

An organic electroluminescence element with a light-emitting layer comprising a gradient concentration of hole transporting and electron-transporting materials, where the concentration of hole transporting materials decreases from the anode to the cathode, and electron-transporting host materials decrease from the cathode to the anode, optimizing the distribution of these materials to enhance light emission across the entire layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a light-emitting layer with uniform material distribution is used, then the structure is simple and easy to manufacture, but light emission is localized and the entire layer is not effectively utilized

Engineering Contradiction:

Improveease of manufactureVSAvoidlight-emission efficiency

Core Design Contradiction:

Ease of manufactureVSProductivity

Solution Approach 1:

The patent applies local quality by creating a light-emitting layer with non-uniform concentration distribution of hole transporting and electron-transporting materials. The concentration of hole transporting material decreases from anode to cathode, while electron-transporting material concentration increases from anode to cathode, optimizing carrier injection and transport at different locations to achieve efficient light emission throughout the entire layer.

Inventive Principle:

Principle #3Local quality

2Illumination intensity

If the concentration of hole transporting light-emitting material is high throughout the layer, then light emission is enhanced, but exciton formation becomes localized and recombination efficiency decreases

Engineering Contradiction:

Improvelight emission intensityVSAvoidrecombination efficiency

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The patent applies parameter changes by varying the concentration of hole transporting light-emitting material and electron-transporting host material throughout the light-emitting layer. The concentration of hole transporting material decreases from anode to cathode, while electron-transporting material concentration increases, creating optimal conditions for carrier recombination and exciton formation at different positions to maintain high light emission efficiency throughout the layer.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If a barrier layer is introduced between light-emitting layer and hole transport layer, then carrier migration balance is improved, but driving voltage increases and brightness decreases

Engineering Contradiction:

Improvecarrier migration balanceVSAvoiddriving voltage

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

Instead of introducing a barrier layer that would increase driving voltage, the patent applies local quality by creating a concentration gradient within the light-emitting layer itself. The hole transporting light-emitting material concentration is higher near the anode to facilitate hole injection, then decreases toward the cathode, while electron-transporting material concentration increases, creating optimal local conditions for carrier balance without additional voltage penalty.

Inventive Principle:

Principle #3Local quality

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 configuration results in improved light-emission efficiency and durability by facilitating recombination throughout the light-emitting layer, reducing localized exciton formation, and maintaining high efficiency even at high brightness levels.

Implementation Method 1

The organic EL element is a device for obtaining luminescence by utilizing at least either one of luminescence from excitons each of which is obtained by recombining an electron injected from a cathode with a hole injected from an anode to produce the exciton in the light-emitting layer

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 2

a concentration of the hole transporting light-emitting material in the light-emitting layer decreases from an anode side toward a cathode side

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentUS8106581B2Organic electroluminescence element having concentration variation of hole transporting light-emitting material

Publication Date: 2012.01.31 UDC IRELAND

AI summary

An organic electroluminescence element including an organic layer including a light-emitting layer disposed between a pair of electrodes, wherein the light-emitting layer contains at least one hole transporting light-emitting material and at least one electron-transporting host material, and a concentration of the hole transporting light-emitting material in the light-emitting layer decreases from an anode side toward a cathode side.