Organic Electroluminescent Element with Segmented Emission Layers

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Solution Overview

Problem

Organic electroluminescence devices using the TADF mechanism face efficiency roll-off at high current densities and lack configurations with multiple emitting layers, limiting their practical application.

Innovation Solution

An organic electroluminescence device with a pair of electrodes and multiple emitting layers, where the first emitting layer includes a host material with a small energy gap between singlet and triplet states, and the second emitting layer emits light at different wavelengths, achieving white emission through additive color mixing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a single emitting layer with TADF mechanism is used, then internal quantum efficiency can reach theoretical maximum, but luminous efficiency roll-off occurs at high current densities

Engineering Contradiction:

Improveinternal quantum efficiencyVSAvoidluminous efficiency roll-off

Core Design Contradiction:

Use of energy by moving objectVSLoss of energy

Solution Approach 1:

The emitting layer is divided into multiple emitting layers (first emitting layer with TADF mechanism, second emitting layer with different luminescent material) having different energy level structures. This segmentation allows each layer to operate under different mechanisms, preventing the efficiency roll-off that occurs in single-layer TADF devices at high current densities while maintaining high internal quantum efficiency.

Inventive Principle:

Principle #1Segmentation

2Duration of action of stationary object

If fluorescent emission mechanism is used, then device lifetime is extended, but internal quantum efficiency is limited to 25%

Engineering Contradiction:

Improvedevice lifetimeVSAvoidinternal quantum efficiency

Core Design Contradiction:

Duration of action of stationary objectVSUse of energy by moving object

Solution Approach 1:

The patent combines fluorescent emission mechanism (first emitting layer with TADF) and phosphorescent emission mechanism (second emitting layer with different luminescent material) in a single device. This merging allows the device to utilize both singlet and triplet excitons effectively, achieving internal quantum efficiency exceeding 25% while maintaining the extended lifetime characteristics of fluorescent devices.

Inventive Principle:

Principle #5Merging (Combining)

3Use of energy by moving object

If phosphorescent emission mechanism is used, then internal quantum efficiency reaches 100%, but device lifetime is reduced

Engineering Contradiction:

Improveinternal quantum efficiencyVSAvoiddevice lifetime

Core Design Contradiction:

Use of energy by moving objectVSDuration of action of stationary object

Solution Approach 1:

Different regions (emitting layers) of the device are assigned different emission characteristics: the first emitting layer uses TADF mechanism with local singlet-triplet energy gap control for high efficiency and lifetime, while the second emitting layer uses phosphorescent materials for complementary emission. This local quality differentiation allows the overall device to achieve both high internal quantum efficiency and extended lifetime.

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

The device exhibits enhanced luminous efficiency and maintains high performance at high current densities by utilizing the TADF mechanism and additive color mixing, potentially achieving theoretical internal quantum efficiencies of 100%.

Implementation Method 1

The TADF mechanism utilizes a phenomenon in which inverse intersystem crossing from triplet excitons to singlet excitons is generated by using a material having a small energy gap (ΔST) between the singlet level and the triplet level. Inverse intersystem crossing from triplet excitons to singlet excitons is generated by using a material having a small energy gap (ΔST) between the singlet level and the triplet level

Methodology Applied

Scientific EffectThermally Activated Delayed Fluorescence (TADF):

Implementation Method 2

When voltage is applied on an organic electroluminescence device, holes and electrons are respectively injected into an emitting layer from an anode and a cathode. The injected electrons and holes are recombined in an emitting layer to form excitons.

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 3

the second emitting layer emits light at different wavelengths, achieving white emission through additive color mixing

Methodology Applied

Scientific EffectAdditive Color Mixing:

Data Source

PatentUS9899620B2Organic electroluminescent element

Publication Date: 2018.02.20 IDEMITSU KOSAN CO LTD

AI summary

An organic electroluminescence device includes a pair of electrodes and an organic compound layer interposed therebetween. The organic compound layer includes a plurality of emitting layers at least including a first emitting layer and a second emitting layer. The first emitting layer contains a first host material and a fluorescent first luminescent material. The second emitting layer contains a second luminescent material that is different from the first luminescent material. A difference ΔST(H1) between singlet energy EgS(H1) of the first host material and an energy gap Eg77K(H1) at 77[K] of the first host material satisfies a specific relationship. One of the first luminescent material and the second luminescent material has a main peak wavelength from 400 nm to less than 500 nm and the other of the first luminescent material and the second luminescent material has a main peak wavelength from 500 nm to 700 nm.