Stacked Light-Emitting Layer Exciplex Energy Transfer

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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 emission efficiency.

Innovation Solution

A light-emitting element with a stacked-layer structure comprising a first and second light-emitting layer, each containing a light-emitting substance, host, and assist materials that form exciplexes, optimizing energy transfer by aligning the emission spectra of the host and assist materials to overlap with the absorption spectra of the light-emitting substances, enhancing external quantum efficiency and extending the element's lifetime.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

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

Engineering Contradiction:

Improveexternal quantum efficiencyVSAvoidlight extraction efficiency

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The light-emitting layer is divided into multiple stacked sub-layers, each containing different light-emitting substances with complementary emission spectra. This segmentation allows each sub-layer to contribute to different wavelength ranges, collectively achieving broader and more efficient light extraction while reducing energy loss through multiple pathways.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs composite material structures where host materials, guest materials, and assist materials are combined in specific configurations. The host-guest-assist material system creates exciplexes that facilitate efficient energy transfer from triplet excited states to light-emitting species, significantly improving external quantum efficiency beyond the conventional 25% limit.

Inventive Principle:

Principle #40Composite materials

2Duration of action of stationary object

If conventional single-layer light-emitting structures are used, then device complexity is low, but energy transfer efficiency is insufficient leading to limited lifetime

Engineering Contradiction:

Improveelement lifetimeVSAvoidlight-emitting layer structure

Core Design Contradiction:

Duration of action of stationary objectVSDevice complexity

Solution Approach 1:

The light-emitting layer is segmented into multiple functional sub-layers with distinct roles: host materials for charge transport, guest materials for light emission, and assist materials for energy transfer. This segmentation enables optimized energy transfer pathways that reduce non-radiative recombination and extend element lifetime, despite the increased structural complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Assist materials serve as intermediaries that facilitate efficient energy transfer from the host triplet excited states to the guest light-emitting substances. These intermediary species create exciplexes that bridge the energy gap, enabling effective triplet-to-singlet energy transfer and reducing energy loss, thereby extending operational lifetime.

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

The proposed structure significantly increases external quantum efficiency and extends the lifetime of light-emitting elements by facilitating efficient energy transfer and reducing deactivation of excitation energy, leading to improved emission efficiency and longer operational life.

Implementation Method 1

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

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 2

a combination of the first organic compound (host material) and the second organic compound (assist material) forms an exciplex

Methodology Applied

Scientific EffectEnergy transfer:

Data Source

PatentUS11393997B2Light-emitting element, light-emitting device, electronic device, and lighting device

Publication Date: 2022.07.19 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 first organic compound, and a third organic compound having a hole-transport property. The second organic compound has a lower HOMO 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 first and the third organic compounds form an exciplex.