Fluorene Compound Hole-Transport Layer for OLED Efficiency

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Solution Overview

Problem

Conventional light-emitting elements using organic electroluminescence face issues with low light extraction efficiency due to materials like NPB absorbing visible light, poor thermophysical properties, and inefficient carrier balance, leading to quenching and color changes.

Innovation Solution

A fluorene compound with a wide band gap and high triplet excitation energy is introduced, which can be used as a hole-transport layer to prevent energy transfer and improve carrier injection, enhancing emission efficiency and lifetime.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If NPB is used as a carrier-transport layer material, then carrier transport is improved, but light extraction efficiency deteriorates due to visible light absorption

Engineering Contradiction:

Improvecarrier transportVSAvoidlight extraction efficiency

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent changes the optical parameter (band gap) of the carrier-transport layer material by selecting a fluorene compound with a wide band gap of 3.8 eV or more, ensuring no visible light absorption while maintaining carrier transport functionality

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the conventional NPB material with a fluorene compound that has superior properties (wide band gap, high T1 level) and can be deposited as a thin film, effectively creating a new material solution that eliminates the light absorption problem

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If materials with wide band gap are used to prevent energy transfer, then quenching is reduced, but thermophysical properties deteriorate due to low molecular weight

Engineering Contradiction:

Improveenergy transfer preventionVSAvoidthermophysical properties

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent creates a composite molecular structure by combining a fluorene core (providing wide band gap and high T1 level) with aromatic amine groups (providing high molecular weight and good thermophysical properties), achieving both energy transfer prevention and thermal stability

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent merges the functional benefits of two different material classes: the optical properties of fluorene compounds (wide band gap, high T1) and the thermophysical properties of aromatic amine compounds (high molecular weight, good film formation), creating a unified material that exhibits both sets of desirable characteristics

Inventive Principle:

Principle #5Merging (Combining)

3Productivity

If carrier-injection barrier is increased to suppress carrier passage, then recombination efficiency is improved, but device complexity increases due to multiple layers

Engineering Contradiction:

Improverecombination efficiencyVSAvoidlayer structure

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The fluorene compound performs multiple functions simultaneously: it acts as a carrier-transport layer with appropriate injection barrier, and also prevents energy transfer to the electrode due to its wide band gap and high T1 level, eliminating the need for separate functional layers

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 fluorene compound improves light-emitting element efficiency by reducing light absorption, maintaining carrier balance, and extending the device's lifespan.

Implementation Method 1

a material (an exciton-blocking material) having higher excitation energy than a light-emitting layer is preferably used for a carrier-transport layer which is adjacent to the light-emitting layer so that excitation energy is not transferred from the light-emitting layer

Methodology Applied

Scientific EffectEnergy transfer prevention:

Implementation Method 2

application of a voltage to the light-emitting element causes injection of electrons from the cathode and holes from the anode into the layer containing the organic compound having a light-emitting property

Methodology Applied

Scientific EffectCarrier injection:

Implementation Method 3

a current flows. Light is emitted when the carriers (electrons and holes) are recombined

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 4

In a basic structure of such a light-emitting element, a layer containing a light-emitting substance is interposed between a pair of electrodes. By applying voltage to this element, light emission from the light-emitting substance can be obtained

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS9564597B2Fluorene compound, light-emitting element, light-emitting device, electronic device, lighting device, and organic compound

Publication Date: 2017.02.07 SEMICON ENERGY LAB CO LTD

AI summary

A substance having a hole-transport property and a wide band gap is provided. A fluorene compound represented by a general formula (G1) is provided. In the general formula (G1), α1 and α2 separately represent a substituted or unsubstituted arylene group having 6 to 13 carbon atoms; Ar1 represents a substituted or unsubstituted aryl group having 6 to 18 carbon atoms, a substituted or unsubstituted 4-dibenzothiophenyl group, or a substituted or unsubstituted 4-dibenzofuranyl group; n and k separately represent 0 or 1; Q1 represents sulfur or oxygen; and R1 to R15 separately represent hydrogen, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 14 carbon atoms.