Cross-linked Charge Transport Layer for OLED Efficiency

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Solution Overview

Problem

Organic light-emitting devices (OLEDs) face challenges in achieving high internal quantum efficiency due to non-radiative decay mechanisms, particularly at room temperature, where triplet excitons often lose energy as heat rather than emitting light, limiting their luminescent efficiency.

Innovation Solution

Incorporating a covalently cross-linked matrix of organic charge transport material with a dopant in the organic layer, which enhances the stability and reduces non-radiative decay, allowing for efficient phosphorescent emission from triplet excited states by confining the organic molecule close to an atom of high atomic number, leveraging the heavy atom effect for improved spin-orbit coupling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of stationary object

If a conventional organic charge transport layer is used, then the device can be fabricated simply, but the device lifetime is short and luminescent efficiency is limited due to non-radiative decay of triplet excitons

Engineering Contradiction:

Improvedevice lifetimeVSAvoidlayer structure complexity

Core Design Contradiction:

Duration of action of stationary objectVSDevice complexity

Solution Approach 1:

The patent employs a composite charge transport layer comprising a host material (e.g., NPB or TPD) doped with a triplet stabilizing material (e.g., Alq3 or BCP). This composite structure enables the layer to simultaneously perform charge transport and triplet exciton stabilization functions, thereby extending device lifetime and enhancing luminescent efficiency without requiring additional separate layers

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent modifies the compositional parameters of the charge transport layer by incorporating specific dopant concentrations (e.g., 5-20 wt% Alq3 or BCP) into the host material. This parameter change enables the material to stabilize triplet excitons through heavy atom effect and spin-orbit coupling, converting non-radiative decay pathways into radiative phosphorescent emission, thus extending device lifetime while maintaining structural simplicity

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If triplet excitons are used for light emission, then internal quantum efficiency can be improved, but non-radiative decay at room temperature causes energy loss as heat

Engineering Contradiction:

Improveinternal quantum efficiencyVSAvoidenergy loss as heat

Core Design Contradiction:

Use of energy by moving objectVSLoss of energy

Solution Approach 1:

The patent converts the harmful non-radiative decay of triplet excitons into beneficial phosphorescent light emission. By incorporating triplet stabilizing materials with heavy atoms (e.g., Alq3 containing aluminum, BCP containing boron), the patent enhances spin-orbit coupling, which allows triplet excitons to transition to singlet states and emit photons radiatively, thus converting energy that would otherwise be lost as heat into useful light output

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The triplet stabilizing material acts as an intermediary between the charge transport host and the triplet excitons. Materials like Alq3 and BCP mediate the interaction by providing heavy atom effects that enhance spin-orbit coupling, facilitating the conversion of triplet excitons into radiative emissions while the host material continues to perform charge transport functions

Inventive Principle:

Principle #24Intermediary (Mediator)

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 significantly extends the device lifetime and maintains high luminescent efficiency, as demonstrated by a 220-hour luminance decay to 80% of initial brightness compared to 71 hours without the dopant, while maintaining performance and efficiency comparable to undoped devices.

Implementation Method 1

confining the organic molecule close to an atom of high atomic number, leveraging the heavy atom effect for improved spin-orbit coupling

Methodology Applied

Scientific EffectHeavy atom effect:

Implementation Method 2

leveraging the heavy atom effect for improved spin-orbit coupling

Methodology Applied

Scientific EffectSpin-orbit coupling:

Implementation Method 3

non-radiative decay mechanisms, particularly at room temperature, where triplet excitons often lose energy as heat

Methodology Applied

Scientific EffectNon-radiative decay:

Data Source

PatentUS7825587B2Charge transporting layer for organic electroluminescent device

Publication Date: 2010.11.02 UNIVERSAL DISPLAY CORP

AI summary

Organic devices comprising an organic layer, wherein the organic layer comprises: (a) a host material formed of a covalently cross-linked matrix comprising an organic charge transport material, and (b) a dopant. The charge transport material has reactive groups for forming cross-links. The cross-linked matrix may allow the organic layer to be solvent resistant. The dopant may protect the cross-linked matrix from electrochemical degradation. The dopant may be a charge acceptor and/or capable of forming covalent bonds with free reactive groups on the cross-linked charge transport material.