OLED Device with Phosphorescent Host for Low Voltage Efficiency

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Solution Overview

Problem

Current organic light-emitting diode (OLED) devices face limitations in achieving low voltage and high luminance efficiency, particularly due to the inefficiency in utilizing triplet excitons, which are not readily used in the light emission process.

Innovation Solution

The use of an organic light-emitting device with a light-emitting layer comprising an organometallic host material and a phosphorescent light-emitting compound, where the triplet energy of the phosphorescent compound is less than or equal to the triplet energy of the host material, allowing for efficient energy transfer and emission from both singlet and triplet excitons.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a conventional organic EL device uses only fluorescent emission from singlet excitons, then the device structure is simple, but the luminance efficiency is low because only 25% of excitons are utilized

Engineering Contradiction:

Improveluminance efficiencyVSAvoiddevice structure

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent changes the emission mechanism parameter from purely fluorescent (singlet) to phosphorescent (triplet) by introducing phosphorescent dopants and adjusting host-guest energy level relationships, enabling utilization of both singlet and triplet excitons for light emission

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material systems combining host materials with phosphorescent dopants (such as Ir(ppy)3) to create a light-emitting layer that can harvest both singlet and triplet excitons, achieving high efficiency electroluminescence

Inventive Principle:

Principle #40Composite materials

2Illumination intensity

If the organic layers are made very thick to ensure sufficient light emission, then the emission intensity is high, but the operating voltage becomes very high (>100V)

Engineering Contradiction:

Improveemission intensityVSAvoidoperating voltage

Core Design Contradiction:

Illumination intensityVSUse of energy by moving object

Solution Approach 1:

The patent changes the layer thickness parameter from micrometer scale (>1 μm) to nanometer scale (few hundred nanometers) while simultaneously changing the emission mechanism to phosphorescence, which maintains high emission intensity at low voltages due to efficient triplet exciton utilization

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs extremely thin organic layers (few hundred nanometers) with phosphorescent emission to achieve high luminance at low operating voltages, replacing the thick layers required for fluorescent emission

Inventive Principle:

Principle #30Flexible shells and thin films

3Loss of energy

If triplet excitons are not utilized in the light emission process, then the device structure is simple, but 75% of excitons are lost resulting in low efficiency

Engineering Contradiction:

Improveexciton utilization efficiencyVSAvoidlight-emitting layer composition

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent converts the previously harmful non-emissive triplet excitons into beneficial light-emitting species by introducing phosphorescent dopants that can emit from triplet states, thereby harvesting the 75% of excitons that were previously lost

Inventive Principle:

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

Solution Approach 2:

The patent introduces phosphorescent dopants as intermediary substances that mediate energy transfer from both singlet and triplet excitons to produce phosphorescent emission, enabling efficient utilization of all excitons

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 results in improved luminance efficiency and reduced operating voltage, enhancing the overall performance of OLED devices by effectively utilizing both singlet and triplet excitons for light emission.

Implementation Method 1

If the triplet state of the dopant is emissive, it can produce light by phosphorescence

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 2

triplet excitons can transfer their energy to a dopant

Methodology Applied

Scientific EffectEnergy transfer:

Implementation Method 3

The excited singlet state is created when excitons formed in an OLED device transfer their energy to the excited state of the dopant

Methodology Applied

Scientific EffectEnergy transfer:

Implementation Method 4

The singlet excited state can often relax, by an intersystem crossing process, to the emissive triplet excited state

Methodology Applied

Scientific EffectIntersystem crossing:

Data Source

PatentEP1920481B1Electroluminescent device with red triplet emitter

Publication Date: 2016.10.12 GLOBAL OLED TECHNOLOGY LLC

AI summary

An organic light-emitting device contains a cathode, an anode, and having located there-between a light-emitting layer, comprising: a) a host material including an organometallic compound represented by Formula (1): wherein: R1 through R6 each independently represent hydrogen or a substituent group, and L represents a substituent; and b) at least one phosphorescent light-emitting compound, with a triplet energy less than or equal to the triplet energy of the host material. The device provides an improved combination of low voltage and luminance efficiency.