Organic Electroluminescent Device Hole Injection Layer Optimization

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Solution Overview

Problem

Organic electroluminescent devices, particularly those emitting blue and green light, face challenges in achieving high light emitting efficiency and durability due to charge stagnation at layer interfaces, leading to material deterioration.

Innovation Solution

An organic electroluminescent device structure is developed with a hole injection-promoting layer of specific thickness (0.1 nm to 3 nm) and ionization potential relationships between layers, enhancing hole injection and reducing electron injection to prevent material decomposition, thereby improving durability and efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a hole flow rate-suppressing layer is formed to adjust carrier recombination balance, then light emitting efficiency is improved, but charge stagnation occurs at layer interfaces accelerating material deterioration

Engineering Contradiction:

Improvelight emitting efficiencyVSAvoidoperational durability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the ionization potential parameter of the hole-transporting layer to be lower than that of the light-emitting layer, reversing the conventional approach. This parameter change enables effective hole injection while preventing charge stagnation, thus improving both light emitting efficiency and operational durability simultaneously

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent inverts the conventional ionization potential relationship between layers. Instead of having the hole-transporting layer with higher IP than the light-emitting layer (conventional approach), it uses a lower IP for the hole-transporting layer, which prevents charge stagnation while maintaining efficient hole transport and injection

Inventive Principle:

Principle #13The other way round (Inversion)

2Productivity

If hole injection is promoted with higher IP in hole-transporting layer, then hole injection efficiency is improved, but charge stagnation at interfaces accelerates material deterioration

Engineering Contradiction:

Improvehole injection efficiencyVSAvoidcharge stagnation

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the ionization potential parameter relationship between layers, setting the hole-transporting layer IP lower than the light-emitting layer IP. This parameter change promotes effective hole injection while preventing charge stagnation at the interface, eliminating the harmful effect without sacrificing injection efficiency

Inventive Principle:

Principle #35Parameter changes

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 solution achieves high light emitting efficiency and operational durability, particularly for blue phosphorescence emission, by optimizing the ionization potential and thickness of the hole injection-promoting layer, suppressing charge stagnation and material deterioration.

Implementation Method 1

emitting light based on electroluminescence from an exciton, produced by recombination in the light-emitting layer of an electron injected from a cathode and a hole injected from an anode

Methodology Applied

Scientific EffectHole injection: Electroluminescence

Implementation Method 2

a hole-transporting layer containing a hole-transporting material

Methodology Applied

Scientific EffectCharge transport: Conduction (electrical)

Implementation Method 3

emitting light based on electroluminescence from an exciton, produced by recombination in the light-emitting layer

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS7923128B2Organic electroluminescent device

Publication Date: 2011.04.12 UDC IRELAND

AI summary

The invention provides an organic electroluminescent device having at least a light-emitting layer containing a light-emitting material and a host material, a hole injection-promoting layer, and a hole-transporting layer containing a hole-transporting material in this order between a pair of electrodes, in which the hole injection-promoting layer contains a hole-transporting material and has a thickness of 0.1 nm to 0.3 nm, and the relationship Ip1<Ip2<Ip3 is satisfied, when Ip1 is defined as the ionization potential of the hole-transporting material of the hole-transporting layer, Ip2 is defined as the ionization potential of the hole-transporting material of the hole injection-promoting layer, and Ip3 is defined as the ionization potential of the host material. Accordingly, the invention provides an electroluminescent device excellent in both light emitting efficiency and operation durability.