Organic Electroluminescent Element Intermediate Layer Electron Trapping

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Solution Overview

Problem

Current organic electroluminescent elements face a short lifetime due to excess electrons damaging the hole transport layer, as the number of electrons supplied to the light emitting layer is not adequately controlled, leading to deterioration of the organic materials.

Innovation Solution

Incorporating an intermediate layer with a lower lowest unoccupied molecular orbital (LUMO) energy level than the hole transport and light emitting layers to trap excess electrons, and a hole injection layer with a suitable energy level difference to enhance electron and hole recombination, thereby reducing electron entry into the hole transport layer and improving light emitting efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If the number of electrons supplied to the light emitting layer is increased to obtain sufficient emission brightness, then the emission brightness is improved, but excess electrons damage the hole transport layer, resulting in a shorter lifetime

Engineering Contradiction:

Improveemission brightnessVSAvoidlifetime

Core Design Contradiction:

Illumination intensityVSDuration of action of stationary object

Solution Approach 1:

An electron transport layer is introduced as an intermediary between the cathode and the light emitting layer. This layer has a LUMO energy level lower than that of the light emitting layer, creating an energy barrier that prevents excess electrons from entering the hole transport layer while still allowing sufficient electrons to reach the light emitting layer for brightness generation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The energy level parameters (LUMO levels) of the electron transport layer are specifically designed to be lower than those of the light emitting and hole transport layers. This parameter change creates an energy cascade that controls electron flow, enabling high brightness while protecting the hole transport layer from electron damage.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If amine derivative materials are used in the hole transport layer to transport holes, then hole transport capacity is improved, but electrons destroy the molecular structure of the amine, causing deterioration and shorter lifetime

Engineering Contradiction:

Improvehole transport capacityVSAvoidlifetime

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The electron transport layer serves as a protective intermediary that blocks excess electrons from reaching the amine derivative materials in the hole transport layer. This mediation allows the amine derivatives to maintain their excellent hole transport capacity without suffering from electron-induced molecular destruction.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The lower LUMO energy level of the electron transport layer, which initially seems to facilitate electron flow, actually creates an energy barrier that protects the hole transport layer. The electron transport layer absorbs the harmful effect by being the first to receive electrons, converting potential damage to the hole transport layer into a protective function.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 increases the lifetime of the organic electroluminescent element by reducing electron-induced deterioration of the hole transport layer and enhancing light emitting efficiency through improved recombination of electrons and holes.

Implementation Method 1

the intermediate layer has an energy level of a lowest unoccupied molecular orbital lower than energy levels of lowest unoccupied molecular orbitals of the hole transport layer and the light emitting layer

Methodology Applied

Scientific EffectEnergy level difference (LUMO):

Implementation Method 2

a light emitting layer for emitting light by facilitating to recombine holes transported through the hole transport layer with electrons

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS8153275B2Organic electroluminescent element and display device or light emitting device equipped with the same

Publication Date: 2012.04.10 SANYO ELECTRIC CO LTD

AI summary

It is an object of the present invention to provide an organic electroluminescent element having a longer lifetime. In order to accomplish the object, an organic electroluminescent element adapted to comprise a light emitting layer including an organic material between an anode and a cathode is provided with a hole transport layer for transporting holes injected from the anode toward the light emitting layer. Along with the hole transport layer, an intermediate layer having an energy level of a lowest unoccupied molecular orbital lower than those of the hole transport layer and the light emitting layer is provided therebetween.