Organic EL Light Emitting Device with Intermediate Layers for Luminance Balance
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Solution Overview
Problem
Existing organic electroluminescent (EL) devices face luminance imbalance and reduced service life due to high electron transportability compared to hole transportability, leading to concentration of recombination sites and luminance deterioration in the second light emitting layer.
Innovation Solution
Incorporating a first and second intermediate layer with specific host and assist dopant materials and concentrations, and adjusting the thickness of the second intermediate layer to balance carrier transportability and recombination sites across the light emitting layers, thereby distributing the recombination site and reducing luminance deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a material having high electron transportability is used for the first intermediate layer, second light emitting layer, second intermediate layer, and third light emitting layer to ensure smooth electron supply, then electron transportability is improved, but the recombination site concentrates at the interface between the first intermediate layer and second light emitting layer, causing luminance deterioration and reduced service life
Solution Approach 1:
The patent applies local quality by introducing an assist dopant material specifically in the second light emitting layer and second intermediate layer to create localized carrier transportability adjustment. This allows the second light emitting layer to have balanced electron and hole transportability while other layers maintain high electron transportability, preventing recombination site concentration and extending service life.
Solution Approach 2:
The patent changes the carrier transportability parameter by adding an assist dopant material with carrier transportability opposite to the host material. This dopant adjusts the electron and hole transportability balance in specific layers, shifting the recombination site distribution to prevent luminance deterioration while maintaining overall device performance.
2Illumination intensity
If intermediate layers are added to reduce exciton energy transfer between light emitting layers, then luminance balance is improved, but device complexity increases
Solution Approach 1:
The patent uses intermediate layers as mediators between light emitting layers to control exciton energy transfer. These intermediate layers contain specific host materials and assist dopant materials that regulate carrier transport and exciton diffusion, achieving luminance balance while maintaining a manageable layer structure through targeted material selection.
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 effectively suppresses luminance imbalance and extends the service life of the light emitting device by ensuring balanced white light emission and efficient energy transfer between layers.
Implementation Method 1
by a drive circuit, an electric field is applied between the anode and the cathode to inject electrons from the cathode into the light emitting layer and holes from the anode into the light emitting layer. The electrons and the holes then recombine in the light emitting layer, that is, carriers recombine, to generate excitons. When the excitons return to a ground state, the energy is released in the form of light.
Implementation Method 2
a first intermediate layer disposed between the first light emitting layer and the second light emitting layer and configured to adjust a transfer of holes and electrons between the first light emitting layer and the second light emitting layer
Data Source
AI summary
Provided is a light emitting device configured to suppress deterioration in a balance of white light emission and increase a service life. The light emitting device includes a red light emitting layer, a blue light emitting layer, a green light emitting layer, a first intermediate layer configured to adjust a transfer of holes and electrons between the red light emitting layer and the blue light emitting layer, and a second intermediate layer configured to adjust the transfer of holes and electrons between the blue light emitting layer and the green light emitting layer. The intermediate layers and the blue light emitting layer each contain an assist dopant material, a concentration of the assist dopant material in the intermediate layers being greater than a concentration of the assist dopant material in the blue light emitting layer.