Organic EL Display Triplet Exciton Blocking Layer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing organic EL display devices using phosphorescence luminescent materials face reduced luminous efficiency and chromaticity changes due to current density dependency, particularly in blue light emitting layers, which affect the overall performance and color purity.
Innovation Solution
Incorporating a low-molecular material connection layer between the blue and other color organic light emitting layers to enhance energy holding and suppress chromaticity changes, while using a phosphorescence luminescent material for improved efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescence luminescent material is used in blue light emitting layer, then internal quantum efficiency is improved (75% or more), but luminous efficiency is actually reduced and chromaticity changes due to current density dependency
Solution Approach 1:
A triplet exciton blocking layer is introduced between the blue phosphorescence light emitting layer and other light emitting layers. This intermediary layer has higher triplet excited level than the phosphorescence luminescent material, preventing triplet exciton diffusion to adjacent layers while allowing singlet excitons to pass through. This resolves the contradiction by maintaining high internal quantum efficiency of phosphorescence material while preventing luminous efficiency reduction and chromaticity changes.
Solution Approach 2:
The patent applies different energy level characteristics to different layers: the triplet exciton blocking layer is specifically designed with higher triplet excited level than the phosphorescence luminescent material to create a localized energy barrier. This local energy level differentiation confines triplet excitons to the blue light emitting layer, ensuring stable luminous efficiency and chromaticity without affecting the overall device structure.
2Use of energy by moving object
If triplet excitons diffuse to adjacent light emitting layers, then energy transfer occurs, but luminous efficiency is reduced and chromaticity changes
Solution Approach 1:
The triplet exciton blocking layer acts as an energy transfer barrier with higher triplet excited level, selectively blocking triplet exciton diffusion while permitting singlet exciton energy transfer. This intermediary structure maintains desired energy transfer for device operation while preventing harmful triplet exciton migration that reduces luminous efficiency and causes chromaticity changes.
Solution Approach 2:
The patent changes the triplet excited level parameter of the blocking layer to be higher than that of the phosphorescence luminescent material. This parameter differentiation creates an energy barrier that confines triplet excitons, preventing their diffusion to adjacent layers and thereby maintaining stable luminous efficiency and chromaticity characteristics.
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 enhances luminous efficiency and maintains color purity by confining excited energies within the red and green light emitting layers, reducing chromaticity changes and improving current density dependency.
Implementation Method 1
an organic EL element using a phosphorescence material as a luminescence material has been reported. The phosphorescence material has an internal quantum efficiency of 75% or more
Implementation Method 2
an organic film of the same is generally deposited by utilizing a dry method (evaporation method) such as a vacuum evaporation method
Data Source
AI summary
Disclosed herein is an organic EL display device, including: a lower electrode provided every first organic EL element for a blue color and every second organic EL element for another color on a substrate; a hole injection/transport layer provided every first and second organic EL elements; a second organic light emitting layer for another color provided on said hole injection/transport layer for said second organic EL element; a connection layer made of a low-molecular material and provided over an entire surface of said hole injection/transport layer for said second organic light emitting layer and said first organic EL element; a first organic light emitting layer for a blue color provided over an entire surface of said connection layer; and an electron injection/transport layer and an upper electrode provided over an entire surface of said organic light emitting layer in order.