9,9-Dimethylfluorene Polymers for Blue OLED Lifetime

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Solution Overview

Problem

Existing polymer OLED displays face a short lifetime for blue emissive materials, and optimizing cathodes to improve blue material lifetime can adversely affect red and green material performance.

Innovation Solution

Incorporating aromatically conjugated 9,9-dimethylfluorene repeat units into opto-electrical polymers, which increases electron affinity and glass transition temperature, enhancing the thermal stability and performance of blue electroluminescent materials, and allowing them to function as both hole transport and emissive units, thereby eliminating the need for separate units.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of stationary object

If a cathode optimized for blue emissive material lifetime is selected, then the lifetime of blue material is improved, but the performance of red and green materials deteriorates

Engineering Contradiction:

Improvelifetime of blue emissive materialVSAvoidperformance of red and green materials

Core Design Contradiction:

Duration of action of stationary objectVSReliability

Solution Approach 1:

The patent applies universality by designing a single cathode configuration (LiF/Al with specific thickness ratios) that universally improves the lifetime of all emissive materials (blue, green, and red) simultaneously, rather than optimizing for blue alone. This multi-functional cathode structure eliminates the need to trade off blue lifetime improvement against red/green performance degradation.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent employs parameter changes by precisely controlling the thickness parameters of the cathode layers (LiF layer at 3-10 nm and Al layer at 50-100 nm) to achieve optimal electron injection properties that benefit all emissive materials. By adjusting these physical parameters, the cathode delivers improved lifetime across the full color spectrum without sacrificing performance of any individual color.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If separate hole transporting polymer and electroluminescent polymer are used, then charge transport and light emission functions are fulfilled, but device complexity increases

Engineering Contradiction:

Improvecharge transport and light emission functionVSAvoidnumber of polymer layers

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies merging by combining the hole transporting polymer and electroluminescent polymer into a single copolymer structure. The copolymer contains both hole transporting units (such as triphenylamine groups) and electroluminescent units (such as fluorene groups) covalently bonded together, allowing both charge transport and light emission functions to be fulfilled within one material layer, thereby reducing device complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The copolymer design embodies multi-functionality by enabling a single polymer material to perform multiple functions: hole transport, electron transport, and electroluminescence. This eliminates the need for separate functional layers and simplifies the overall device architecture while maintaining reliable charge transport and light emission performance.

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 use of 9,9-dimethylfluorene-based polymers significantly increases the lifetime and thermal stability of blue electroluminescent materials, improving device performance and extending the operational lifespan of polymer OLEDs while maintaining or improving the performance of red and green materials.

Implementation Method 1

the polymer comprising aromatically conjugated repeat units of 9,9-dimethylfluorene linked to and conjugated with aromatic rings of adjacent repeat units by a single bond

Methodology Applied

Scientific EffectAromatic conjugation:

Implementation Method 2

The holes and electrons combine in the organic electroluminescent layer to form an exciton which then undergoes radiative decay to give light

Methodology Applied

Scientific EffectRadiative decay:

Implementation Method 3

incorporation of repeat units that increase the glass temperature (Tg) of the polymer. In particular, incorporation of 2,7-linked 9,9-diarylfluorene repeat units into an electroluminescent polymer, particularly a blue emissive electroluminescent polymer, results in significant increase in that polymer's lifetime

Methodology Applied

Scientific EffectGlass transition:

Data Source

PatentEP2016112B1Opto-electrical polymers and devices

Publication Date: 2015.11.18 CDT OXFORD

Figure 1~2
Figure 3

AI summary

A polymer for use in an opto-electrical device comprising aromatically conjugated repeat units of optionally substituted 9,9-dimethylfluorene.