ITO Electrode Work Function Tuning for OLED Hole Injection

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Solution Overview

Problem

Existing organic light emitting diodes (OLEDs) face a high hole injection barrier due to the mismatch between the work function of the anode and the highest occupied molecular orbital (HOMO) of the organic layer, leading to poor operational stability and increased manufacturing costs, as additional organic layers are required to mitigate this barrier.

Innovation Solution

The method involves functionalizing the surface of transparent conducting oxide (TCO) electrodes, such as indium tin oxide (ITO), by reacting them with electronegative species like chlorine using electromagnetic radiation to increase the work function, thereby reducing the hole injection barrier without compromising conductivity or stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If additional organic layers are added to reduce the hole injection barrier, then the hole injection efficiency is improved, but the device cost increases and manufacturing yield decreases

Engineering Contradiction:

Improvehole injection efficiencyVSAvoidnumber of organic layers

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the work function parameter of the ITO electrode from its native value (approximately 4.7 eV) to a higher value (5.0-5.5 eV) through surface functionalization with electronegative species. This parameter change directly reduces the hole injection barrier without requiring additional organic layers, thereby improving hole injection efficiency while maintaining device simplicity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces electronegative species (such as chlorine, fluorine, or oxygen) as intermediary elements that modify the ITO surface properties. These species act as a mediator between the ITO electrode and the organic hole transport layer, creating a more favorable energy level match and reducing the injection barrier without adding complete organic layers

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the work function of the anode is increased to reduce the hole injection barrier, then the hole injection efficiency is improved, but the manufacturing process complexity increases

Engineering Contradiction:

Improvehole injection efficiencyVSAvoidmanufacturing process simplicity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces the mechanical approach of adding multiple organic layers with a chemical/physical surface treatment process. By using plasma treatment, chemical vapor deposition, or atomic layer deposition to functionalize the ITO surface, the manufacturing process achieves the same effect (reduced injection barrier) with fewer material deposition steps

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent performs surface functionalization of the ITO electrode as a preliminary step before depositing the organic layers. This preliminary action modifies the ITO surface properties in advance, ensuring optimal hole injection from the start and eliminating the need for additional organic injection layers that would otherwise be required

Inventive Principle:

Principle #10Preliminary action

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 approach reduces the hole injection barrier, decreases the required operating voltage, and enhances the operational stability and efficiency of OLEDs by aligning the work function of the anode with the HOMO level of the organic layer, potentially eliminating the need for additional organic layers, thus simplifying device construction and reducing costs.

Implementation Method 1

obtaining an electronegative species from a precursor using electromagnetic radiation

Methodology Applied

Scientific EffectPhotodissociation: Photodissociation

Implementation Method 2

reacting a surface of the electrode with the electronegative species

Methodology Applied

Scientific EffectChemical bonding: Chemical Bonding

Implementation Method 3

increasing a work function of an electrode by reacting a surface of the electrode with an electronegative species

Methodology Applied

Scientific EffectWork function modification:

Data Source

PatentUS9853233B2Functionalization of a substrate

Publication Date: 2017.12.26 OTI LUMIONICS INC

AI summary

A method of increasing a work function of an electrode is provided. The method comprises obtaining an electronegative species from a precursor using electromagnetic radiation and reacting a surface of the electrode with the electronegative species. An electrode comprising a functionalized substrate is also provided.