Stacked Light-Emitting Layer Structure for Enhanced Energy Transfer

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Current light-emitting elements have limited external quantum efficiency and lifetime due to inefficient light extraction and energy transfer mechanisms, particularly in phosphorescent compounds where the fluorescence and phosphorescence spectra do not overlap effectively, hindering high energy transfer efficiency.

Innovation Solution

A light-emitting element with a stacked-layer structure comprising a first and second light-emitting layer, each containing specific organic compounds that form exciplexes, enhancing energy transfer efficiency by aligning the emission spectra with the absorption spectra of the light-emitting substances, and utilizing phosphorescent compounds or thermally activated delayed fluorescence materials to convert triplet excitation energy into light emission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If phosphorescent compounds are used to convert triplet excitation energy into light emission, then light emission can be obtained through triplet excited states, but the external quantum efficiency is limited to approximately 25% at most due to light absorption by electrodes and inefficient energy transfer

Engineering Contradiction:

Improveexternal quantum efficiencyVSAvoidenergy transfer efficiency

Core Design Contradiction:

Use of energy by moving objectVSLoss of energy

Solution Approach 1:

The light-emitting layer is divided into multiple sub-layers (first light-emitting layer and second light-emitting layer), each containing different host materials and light-emitting substances. This segmentation allows optimization of energy transfer in each sub-layer, improving overall external quantum efficiency by reducing energy loss through better spectral overlap between host emission and guest absorption in each segment.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs composite material systems combining specific host materials (first organic compound, third organic compound) with light-emitting substances (first light-emitting substance, second light-emitting substance) in each layer. These composite materials are designed to achieve optimal energy transfer through careful selection of materials with complementary spectral properties, thereby improving external quantum efficiency while minimizing energy loss.

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If a single light-emitting layer is used, then the device structure is simple, but the external quantum efficiency and lifetime are limited due to insufficient energy transfer optimization

Engineering Contradiction:

Improveexternal quantum efficiencyVSAvoidlight-emitting layer structure

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the light-emitting layer are assigned different material compositions and properties. The first light-emitting layer uses specific host-guest combinations optimized for certain wavelengths, while the second light-emitting layer uses different combinations for other wavelengths. This local quality differentiation enables each region to contribute optimally to overall device performance, improving external quantum efficiency without requiring excessive complexity.

Inventive Principle:

Principle #3Local quality

3Use of energy by moving object

If the fluorescence and phosphorescence spectra do not overlap effectively, then the device structure can be simpler, but the energy transfer efficiency is hindered, reducing light emission efficiency

Engineering Contradiction:

Improvelight emission efficiencyVSAvoidenergy transfer efficiency

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent systematically adjusts critical parameters including the spectral overlap between host fluorescence and phosphorescence, the energy levels of host and guest materials, and the composition ratios in each light-emitting layer. By optimizing these parameters, the energy transfer efficiency is significantly improved, enabling more effective conversion of triplet excitation energy into light emission and thereby enhancing light emission efficiency while maintaining reliable energy transfer.

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 proposed structure significantly increases external quantum efficiency and extends the lifetime of light-emitting elements by optimizing energy transfer and emission spectra overlap, leading to improved light emission efficiency and reduced deactivation of excitation energy.

Implementation Method 1

In the first light-emitting layer, a combination of the first organic compound (host material) and the second organic compound (assist material) forms an exciplex

Methodology Applied

Scientific EffectExciplex formation:

Implementation Method 2

the first light-emitting layer is formed on the anode side and contains at least a first light-emitting substance (guest material) converting triplet excitation energy into light emission

Methodology Applied

Scientific EffectEnergy transfer:

Implementation Method 3

a first light-emitting substance (guest material) converting triplet excitation energy into light emission

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 4

in the second light-emitting layer, a combination of the third organic compound (host material) and the second organic compound (assist material) forms an exciplex

Methodology Applied

Scientific EffectExciplex formation:

Implementation Method 5

the second light-emitting layer contains at least a second light-emitting substance (guest material) converting triplet excitation energy into light emission

Methodology Applied

Scientific EffectEnergy transfer:

Implementation Method 6

a second light-emitting substance (guest material) converting triplet excitation energy into light emission

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Data Source

PatentUS9299944B2Light-emitting element, light-emitting device, electronic device, and lighting device

Publication Date: 2016.03.29 SEMICON ENERGY LAB CO LTD

AI summary

A light-emitting layer, which is a stack of a first light-emitting layer and a second light-emitting layer, is provided between an anode and a cathode. The first light-emitting layer is formed on the anode side and contains a first light-emitting substance converting triplet excitation energy into light emission, a first organic compound having an electron-transport property, and a second organic compound having a hole-transport property. The second light-emitting layer contains a second light-emitting substance converting triplet excitation energy into light emission, the second organic compound, and a third organic compound having an electron-transport property. The first organic compound has a higher LUMO level than the third organic compound. The first light-emitting substance emits light with a wavelength shorter than that of light emitted from the second light-emitting substance. The first and the second organic compounds form an exciplex. The second and the third organic compounds form an exciplex.