Blue Organic EL Device Ultraviolet Dopant Efficiency

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Solution Overview

Problem

Current blue organic electroluminescent devices face challenges in achieving high luminous efficiency and current efficiency, particularly in reducing power consumption for flat panel displays, as existing configurations result in decreased luminous efficiency with increased luminance.

Innovation Solution

A blue organic electroluminescent device is designed with an emitting layer containing a host material and multiple dopants, where at least one dopant exhibits ultraviolet luminescent properties, preferably as a heavy metal complex with a triplet energy gap greater than another dopant, and ionization potential lower than the host material, to enhance carrier balance and recombination probability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If conventional phosphorescent dopants are used in the emitting layer, then green or red light emission is achieved, but blue luminous efficiency remains low

Engineering Contradiction:

Improveblue luminous efficiencyVSAvoidcolor range

Core Design Contradiction:

Illumination intensityVSAdaptability or versatility

Solution Approach 1:

The emitting layer is segmented into multiple dopant components with distinct functions: a phosphorescent dopant for triplet state utilization and a fluorescent dopant for blue light emission. This segmentation allows each dopant to optimize its specific function, resolving the contradiction between achieving blue efficiency and maintaining color versatility.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite dopant system combining phosphorescent and fluorescent materials in the emitting layer. This composite approach enables simultaneous exploitation of triplet state energy (from phosphorescent dopant) and efficient blue light emission (from fluorescent dopant), achieving high blue luminous efficiency while maintaining device versatility.

Inventive Principle:

Principle #40Composite materials

2Illumination intensity

If luminance is increased in existing organic EL devices, then brightness is improved, but luminous efficiency significantly decreases

Engineering Contradiction:

ImproveluminanceVSAvoidluminous efficiency

Core Design Contradiction:

Illumination intensityVSUse of energy by moving object

Solution Approach 1:

The invention changes the energy level parameters of the emitting layer by introducing a phosphorescent dopant with appropriate triplet energy and a fluorescent dopant with optimized HOMO/LUMO levels. This parameter optimization enables efficient carrier recombination and exciton utilization across different luminance levels, maintaining high luminous efficiency even at increased luminance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The dual-dopant system ensures continuous useful action by utilizing both singlet and triplet excitons for light emission. The phosphorescent dopant continuously harvests triplet states while the fluorescent dopant emits blue light, maintaining efficient energy conversion across varying operating conditions and luminance levels.

Inventive Principle:

Principle #20Continuity of useful action

3Use of energy by moving object

If power consumption is reduced for flat panel displays, then energy efficiency is improved, but achieving high luminous efficiency becomes more difficult

Engineering Contradiction:

Improvepower consumptionVSAvoidluminous efficiency

Core Design Contradiction:

Use of energy by moving objectVSIllumination intensity

Solution Approach 1:

The invention converts the typically harmful non-radiative decay of triplet excitons into beneficial light emission by introducing a phosphorescent dopant. This dopant enables radiative decay of triplet states, turning what would be energy loss into useful photons, thereby reducing power consumption while maintaining or improving luminous efficiency.

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 achieves high current and luminous efficiency by optimizing the recombination of holes and electrons, leading to improved light emission efficiency and reduced power consumption.

Implementation Method 1

at least one of the dopants having ultraviolet luminescent properties

Methodology Applied

Scientific EffectUltraviolet luminescence: Luminescence

Implementation Method 2

at least one other dopant has visible luminescent properties

Methodology Applied

Scientific EffectVisible luminescence: Luminescence

Implementation Method 3

The electrons recombine with the holes in the emitting layer to produce an excited state, and energy is emitted as light when the excited state returns to the ground state

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS7608993B2Blue organic electroluminescent device comprising dopants having ultraviolet and visible luminescent properties

Publication Date: 2009.10.27 IDEMITSU KOSAN CO LTD

AI summary

A blue organic electroluminescent device (1) including at least an emitting layer (40) between an anode (20) and a cathode (60), the emitting layer (40) including a host material and a plurality of dopants, at least one of the dopants having ultraviolet luminescent properties.