OLED Emissive Layer with Phosphorescent and Fluorescent Emitters

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Solution Overview

Problem

Existing OLED technologies face challenges in achieving efficient light emission with phosphorescent, TADF, and exciplex systems, often resulting in direct charge trapping, red-shifting issues, and poor spectral overlap, which affect the performance and efficiency of organic light emitting diodes.

Innovation Solution

An OLED architecture is developed that incorporates a combination of a phosphorescent emitter, a TADF or exciplex emitter, and a fluorescent emitter, where the phosphorescent emitter acts as a sensitizer, enhancing light emission efficiency and achieving a sharper emission onset and narrower spectral line shape.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If phosphorescent, TADF, and exciplex systems are used for light emission, then internal quantum efficiency can be improved, but emission onset becomes broader and spectral line shape deteriorates

Engineering Contradiction:

Improveinternal quantum efficiencyVSAvoidemission onset sharpness

Core Design Contradiction:

Use of energy by moving objectVSIllumination intensity

Solution Approach 1:

The emissive layer is segmented into three distinct functional components: a phosphorescent emitter for triplet exciton harvesting, a TADF or exciplex emitter for singlet exciton management, and a fluorescent emitter for sharp emission output. This segmentation allows each component to perform its specialized function, resolving the contradiction between efficiency and emission quality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The TADF or exciplex emitter acts as an intermediary between the phosphorescent emitter and the fluorescent emitter. It mediates energy transfer from triplet excitons (harvested by phosphorescent material) to the fluorescent emitter, enabling sharp emission while maintaining high internal quantum efficiency through indirect energy transfer pathways.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If direct charge trapping occurs in phosphorescent, TADF, and exciplex systems, then emission can be achieved, but performance becomes suboptimal

Engineering Contradiction:

Improveemission efficiencyVSAvoidperformance consistency

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

Direct charge trapping is extracted and eliminated from the system by using a host-guest emitter architecture. The emitters are incorporated as dopants in a host matrix, which prevents direct charge trapping on the emitter molecules themselves. Instead, charges are transported through the host material, and energy is transferred to the emitter dopants, significantly improving performance consistency and reliability.

Inventive Principle:

Principle #2Taking out (Extraction)

3Use of energy by moving object

If spectral overlap is increased to improve emission, then internal quantum efficiency improves, but emission onset becomes broader

Engineering Contradiction:

Improveinternal quantum efficiencyVSAvoidspectral line shape

Core Design Contradiction:

Use of energy by moving objectVSShape

Solution Approach 1:

Different regions of the emissive layer are assigned different functional qualities: the phosphorescent emitter provides broad spectral coverage for efficient exciton harvesting, the TADF/exciplex emitter provides intermediate energy transfer, and the fluorescent emitter provides sharp emission lines. This local quality differentiation allows the system to achieve both broad energy absorption and sharp emission output simultaneously.

Inventive Principle:

Principle #3Local quality

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 configuration improves light emission efficiency by harvesting singlet and triplet excitons, resulting in a predominantly fluorescent emission with enhanced internal quantum efficiency and improved spectral characteristics.

Implementation Method 1

The first compound is capable of functioning as a phosphorescent emitter in an OLED at room temperature

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 2

the second compound is capable of functioning as a TADF emitter in an OLED at room temperature

Methodology Applied

Scientific EffectThermally activated delayed fluorescence: Fluorescence

Implementation Method 3

the second compound is capable of forming an exciplex with the first compound in an OLED at room temperature

Methodology Applied

Scientific EffectExciplex emission:

Implementation Method 4

The third compound is a fluorescent compound that functions as an emitter in the OLED of the present disclosure at room temperature

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Data Source

PatentUS20200373510A1Organic electroluminescent materials and devices

Publication Date: 2020.11.26 UNIVERSAL DISPLAY CORP

AI summary

Provided is an OLED that includes in its emissive region a first compound, a second compound, and a third compound, where the first compound is capable of functioning as a phosphorescent emitter in an OLED at room temperature, the second compound meets at least one of the following conditions:(1) the second compound is capable of functioning as a TADF emitter in an OLED at room temperature; and(2) the second compound is capable of forming an exciplex with the first compound in an OLED at room temperature, and the third compound is a fluorescent compound that functions as an emitter in the OLED of the present disclosure at room temperature.