Organic Electroluminescent Device with Concentration Gradient

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Solution Overview

Problem

Existing organic electroluminescent devices face challenges in achieving improved luminescence efficiency and durability due to localized light emission caused by imbalanced carrier distribution in the light emitting layer, where the concentration of light emitting materials leads to excess electrons and insufficient holes, resulting in decreased efficiency and reduced durability.

Innovation Solution

Incorporating a light emitting layer with a light emitting material having hole transportability, a host material with electron transportability, and an electrically inert material, where the concentration of the light emitting material with hole transportability gradually increases from the cathode to the anode side, promoting balanced carrier recombination and uniform light emission across the layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the light emitting layer uses a conventional material composition with uniform concentration, then the device structure is simple, but the carrier distribution becomes imbalanced causing localized light emission and reduced luminescence efficiency

Engineering Contradiction:

Improveluminescence efficiencyVSAvoidlight emitting layer structure

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent applies local quality by creating a concentration gradient of the light emitting material within the light emitting layer. The concentration increases from the cathode side to the anode side, with specific ranges (5-20% near cathode, 60-80% near anode). This non-uniform distribution optimizes carrier recombination locally at different positions, preventing localized light emission and improving overall luminescence efficiency.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the concentration parameter of the light emitting material throughout the layer. Instead of maintaining a constant concentration, the material concentration varies continuously from 5-20% at the cathode interface to 60-80% at the anode interface. This parameter change optimizes the balance between electron and hole injection and recombination, resolving the carrier distribution imbalance.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If the light emitting layer has high concentration of light emitting material, then luminescence efficiency improves, but durability decreases due to excessive electron accumulation

Engineering Contradiction:

Improveluminescence efficiencyVSAvoiddevice durability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent uses local quality to address durability by distributing the light emitting material non-uniformly. High concentration (60-80%) is placed near the anode where hole recombination is more efficient, while lower concentration (5-20%) near the cathode prevents excessive electron accumulation. This spatial differentiation maintains high luminescence efficiency while preventing electron-induced degradation and improving device durability.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If the light emitting material concentration is uniform throughout the layer, then manufacturing is simpler, but carrier recombination is imbalanced leading to localized light emission

Engineering Contradiction:

Improvelight emitting layer fabricationVSAvoidcarrier distribution control

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent implements parameter changes by establishing a controlled concentration gradient of the light emitting material. The concentration transitions from 5-20% at the cathode side to 60-80% at the anode side. This gradient can be achieved through controlled deposition techniques, representing a precise manufacturing parameter that optimizes carrier recombination while remaining feasible to implement.

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

This configuration enhances luminescence efficiency and durability by ensuring balanced electron and hole recombination throughout the light emitting layer, preventing localized light emission and maintaining efficiency even at high luminance levels.

Implementation Method 1

When an electric field is applied to the electrodes, holes and electrons recombine in the light emitting layer 5 in the region sandwiched between the electrodes 3 and 7 to emit light.

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS8362691B2Organic electroluminescent device

Publication Date: 2013.01.29 UDC IRELAND

AI summary

There is provided an organic electroluminescent device 10 having an anode 14, a cathode 18 disposed facing the anode, and an organic layer 16 that is sandwiched between the anode and the cathode and that includes at least a light emitting layer, wherein the light emitting layer includes a light emitting material having hole transportability, a host material having electron transportability and an electrically inert material, and the concentration of the light emitting material having hole transportability gradually increases from the cathode side toward the anode side. Preferably, the concentration of the electrically inert material also gradually increases from the cathode side toward the anode side.