Organic Light Emitting Device Host Material Design

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Solution Overview

Problem

Existing organic light-emitting devices using carbazol compounds as hosts for phosphorescent dopants suffer from low efficiency and short lifetimes, necessitating an improved phosphorescent emission layer with enhanced luminous efficiency and longer lifetime.

Innovation Solution

An organic light-emitting device with an emission layer comprising two different electron transport materials acting as hosts for a phosphorescent dopant, which facilitates efficient recombination of holes and electrons, minimizing energy barriers and preventing carrier traps, thereby increasing luminous efficiency and extending device lifetime.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single electron transport material is used as host for phosphorescent dopant, then device structure is simple, but luminous efficiency is low and lifetime is short

Engineering Contradiction:

Improvedevice lifetimeVSAvoidhost material composition

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The emission layer uses a composite host system comprising two different electron transport materials instead of a single material. This composite structure enables synergistic effects where one material facilitates electron transport while the other provides hole blocking capability, resulting in improved luminous efficiency and extended device lifetime simultaneously.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The first electron transport material serves multiple functions: it acts as the primary electron transport medium and simultaneously provides hole blocking capability. This multi-functionality eliminates the need for separate hole blocking layers, simplifying the overall device structure while maintaining high efficiency and long lifetime performance.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Use of energy by moving object

If phosphorescent materials are used to improve luminous efficiency, then triplet excitons can be utilized, but device lifetime is reduced due to forbidden transition relaxation

Engineering Contradiction:

Improveluminous efficiencyVSAvoiddevice lifetime

Core Design Contradiction:

Use of energy by moving objectVSDuration of action of stationary object

Solution Approach 1:

The invention modifies the energy level parameters of the host materials to create an optimized energy landscape. By carefully selecting materials with specific HOMO and LUMO energy levels, the system achieves efficient triplet exciton utilization while controlling relaxation pathways to extend device operational lifetime.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The first electron transport material acts as an intermediary between the phosphorescent dopant and the second electron transport material. It mediates the interaction by facilitating electron transport to the dopant while blocking holes, thereby enabling efficient phosphorescent emission without the harmful effects of direct hole-dopant interactions that would reduce lifetime.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If energy barriers are minimized in the emission layer, then carrier recombination is enhanced, but material selection and layer design become more complex

Engineering Contradiction:

Improvecarrier recombination efficiencyVSAvoidemission layer design

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The emission layer is designed to create an equipotential region for carriers by positioning the HOMO and LUMO levels of the host materials appropriately. This energy level alignment ensures that electrons and holes can recombine efficiently without encountering significant energy barriers, maximizing carrier recombination efficiency while maintaining a relatively simple two-material structure.

Inventive Principle:

Principle #12Equipotentiality

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 multiple electron transport materials as hosts in the emission layer enhances luminous efficiency and extends the lifetime of organic light-emitting devices, potentially eliminating the need for a hole blocking layer and reducing driving voltage.

Implementation Method 1

phosphorescent materials using triplet excitons having a generation probability of 75% have a better luminous efficiency than fluorescent materials

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 2

The dopant receives energy from the host, thus emitting light

Methodology Applied

Scientific EffectEnergy transfer:

Implementation Method 3

The use of at least two electron transport materials as a host facilitates the re-combination of holes and electrons, thus increasing luminous efficiency

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS7595118B2Organic light emitting device

Publication Date: 2009.09.29 SAMSUNG DISPLAY CO LTD

AI summary

An organic light emitting device including a first electrode, a second electrode, and an emission layer arranged between the first electrode and the second electrode, the emission layer comprising at least two electron transport materials adapted to serve as a host and a phosphorescent dopant. The use of at least two electron transport materials as a host facilitates the re-combination of holes and electrons in neighboring organic layers, thus improving the luminous efficiency and the lifetime of the organic light emitting device.