OLED Spacer Layer Blocks Blue Energy Transfer

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Solution Overview

Problem

The development of a white organic light-emitting diode with high reliability and long life is hindered by the short lifespan of blue phosphorescent emitting dopants, leading to low luminous efficiency and impractical use, as existing configurations struggle to achieve excellent white light emission.

Innovation Solution

An organic light-emitting diode configuration with a blue fluorescent emitting dopant in the blue emissive layer and phosphorescent emitting dopants in the red and green emissive layers, utilizing a spacer layer made of a hole transport material to prevent energy transfer and optimize carrier recombination, resulting in efficient white light emission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If phosphorescent emitting dopants are used for red, green, and blue emissive layers to achieve high luminous efficiency, then internal quantum efficiency can reach nearly 100%, but the blue phosphorescent emitting dopant has short life leading to low reliability

Engineering Contradiction:

Improveinternal quantum efficiencyVSAvoiddiode lifetime

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The emissive layer is segmented into three separate layers (red, green, and blue) with different dopant types. The blue emissive layer uses fluorescent dopant for longevity, while red and green layers use phosphorescent dopants for high efficiency, allowing each layer to be optimized independently for its specific requirements

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the emissive layer have different material compositions and properties. The blue emissive layer has fluorescent characteristics for stability, while red and green layers have phosphorescent characteristics for efficiency, creating local quality variations to resolve the contradiction

Inventive Principle:

Principle #3Local quality

2Reliability

If a blue fluorescent emitting dopant is used in the blue emissive layer to extend lifetime, then reliability improves, but achieving excellent white light emission with high luminous efficiency becomes difficult

Engineering Contradiction:

Improvediode lifetimeVSAvoidluminous efficiency

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The emissive layer is divided into three separate layers (red, green, and blue) with different dopant types. The blue emissive layer uses fluorescent dopant for longevity, while red and green layers use phosphorescent dopants for high efficiency, allowing each layer to be optimized independently for its specific requirements

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent combines fluorescent and phosphorescent emitting dopants in a single device structure, merging the advantages of both types: the stability and longevity of fluorescent materials in the blue layer, and the high internal quantum efficiency of phosphorescent materials in the red and green layers, achieving both reliability and luminous efficiency

Inventive Principle:

Principle #5Merging (Combining)

3Illumination intensity

If carrier recombination is enhanced in both red/green and blue emissive layers to obtain white light emission, then white light output is achieved, but energy transfer between layers causes loss and reduces luminous efficiency

Engineering Contradiction:

Improvewhite light emissionVSAvoidenergy transfer loss

Core Design Contradiction:

Illumination intensityVSLoss of energy

Solution Approach 1:

A spacer layer acts as an intermediary barrier between the blue emissive layer and the red/green emissive layer. This spacer layer prevents direct energy transfer and exciton migration between layers, eliminating the energy loss pathway while still allowing each layer to function independently for white light emission

Inventive Principle:

Principle #24Intermediary (Mediator)

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 enables high luminous efficiency and reliable white light emission by preventing energy transfer and ensuring efficient carrier transportation, improving the practicality of the diode.

Implementation Method 1

the fluorescent emitting dopant converts only singlet excitons into light emission

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Implementation Method 2

the phosphorescent emitting dopant which can convert both singlet and triplet excitons into light emission

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 3

a spacer layer which is inserted between the red and green emissive layer and the blue emissive layer, and consists of a hole transport material which prevents energy transfer from the blue emissive layer to the red and green emissive layer

Methodology Applied

Scientific EffectEnergy transfer blocking:

Data Source

PatentUS8558224B2Organic light-emitting diode, display and illuminating device

Publication Date: 2013.10.15 KK TOSHIBA

AI summary

According to one embodiment, there is provided an organic light-emitting diode including an anode and a cathode which are arranged apart from each other, a red and green emissive layer on the anode side and a blue emissive layer on the cathode side, which are arranged to be separated from each other between the anode and the cathode, and a spacer layer which is inserted between the red and green emissive layer and the blue emissive layer, and consists of a hole transport material which prevents energy transfer from the blue emissive layer to the red and green emissive layer. The red and green emissive layer contains a host material having hole transportability, a red phosphorescent emitting dopant, and a green phosphorescent emitting dopant, and the blue emissive layer contains a host material having electron transportability and a blue fluorescent emitting dopant.