Stacked Light-Emitting Element with Exciplex Layers

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Solution Overview

Problem

Conventional light-emitting elements with stacked fluorescent and phosphorescent layers face challenges in achieving high emission efficiency due to energy transfer issues, leading to reduced performance and increased power consumption.

Innovation Solution

A light-emitting element with a stacked-layer structure comprising a fluorescent layer and a phosphorescent layer, where the phosphorescent layer includes multiple layers forming exciplexes and phosphorescent substances, allowing for efficient energy transfer and emission with a peak wavelength longer than the individual layers, thereby enhancing emission efficiency and reducing power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a fluorescent layer and phosphorescent layer are stacked, then emission efficiency can be improved by utilizing phosphorescence, but triplet excitons generated in the phosphorescent layer are diffused and triplet excitation energy is transferred to the fluorescent layer causing a significant decrease in emission efficiency

Engineering Contradiction:

Improveemission efficiencyVSAvoidtriplet excitation energy transfer loss

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent introduces an intermediary layer between the fluorescent layer and phosphorescent layer to prevent direct energy transfer. This intermediary layer acts as a barrier that blocks triplet exciton diffusion from the phosphorescent layer to the fluorescent layer, thereby preventing the harmful energy transfer while allowing the beneficial phosphorescence emission to occur. The intermediary layer mediates the interaction between the two functional layers, resolving the contradiction between utilizing phosphorescence and preventing energy loss.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If phosphorescent substances are used to improve emission efficiency, then high emission efficiency can be obtained, but power consumption increases

Engineering Contradiction:

Improveemission efficiencyVSAvoidpower consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The patent optimizes the parameters of the phosphorescent layer including the selection of phosphorescent substances with appropriate lifetime characteristics, control of layer thickness, and adjustment of doping concentrations. By carefully controlling these parameters, the device achieves high emission efficiency while minimizing the energy consumption associated with phosphorescence generation and maintaining optimal operational characteristics.

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 solution enables favorable emission efficiency and low power consumption by effectively transferring triplet excitation energy from exciplexes to phosphorescent substances, suppressing exciton diffusion, and increasing the proportion of phosphorescence in emissions, resulting in improved external quantum efficiency and extended device lifetime.

Implementation Method 1

a second light-emitting layer emitting phosphorescent light... The layers in which the exciplexes are formed form a stacked-layer structure in which one layer is sandwiched between and in contact with two layers and emits light with an emission peak wavelength longer than those of light emitted from the two layers

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 2

a light-emitting element containing a phosphorescent substance in which intersystem crossing (i.e., transition from a singlet excited state to a triplet excited state) easily occurs

Methodology Applied

Scientific EffectIntersystem crossing:

Implementation Method 3

suppressing exciton diffusion... effectively transferring triplet excitation energy from exciplexes to phosphorescent substances

Methodology Applied

Scientific EffectExciton diffusion suppression: Diffusion Barrier

Data Source

PatentUS10439158B2Light-emitting element, light-emitting device, electronic appliance, and lighting device

Publication Date: 2019.10.08 SEMICON ENERGY LAB CO LTD

AI summary

A light-emitting element includes a stack of a first light-emitting layer emitting fluorescent light and a second light-emitting layer emitting phosphorescent light between a pair of electrodes. The second light-emitting layer includes a first layer in which an exciplex is formed, a second layer in which an exciplex is formed, and a third layer in which an exciplex is formed. The second layer is located over the first layer, and the third layer is located over the second layer. An emission peak wavelength of the second layer is longer than an emission peak wavelength of the first layer and an emission peak wavelength of the third layer.