Organic EL Display Common Blue Layer Injection Efficiency
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Solution Overview
Problem
The existing organic electroluminescence (EL) displays face issues with low hole or electron injection efficiency from the blue light-emitting layer to the red and green light-emitting layers, resulting in insufficient light emission efficiency and lifetime characteristics for red and green organic EL elements.
Innovation Solution
Incorporating a low-molecular material with a weight-average molecular weight of 50,000 or less into the red and green light-emitting layers, and using a low-molecular material as a common blue light-emitting layer, along with hole and electron injection/transport layers, to improve injection efficiency and interface properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a blue light-emitting layer is arranged over red and green light-emitting layers to reduce manufacturing steps, then manufacturing complexity is reduced, but hole or electron injection efficiency from the blue layer to the red and green layers becomes low
Solution Approach 1:
The patent introduces hole injection/transport layers and electron injection/transport layers as intermediary layers between the blue light-emitting layer and the red/green light-emitting layers. These intermediary layers facilitate efficient charge injection and transport across the interfaces, resolving the low injection efficiency problem while maintaining the simplified common blue layer structure.
Solution Approach 2:
The patent modifies the energy level parameters of the light-emitting layers by selecting materials with appropriate HOMO and LUMO levels. The blue light-emitting layer uses materials with higher energy levels, while the red and green layers use materials with lower energy levels, creating favorable energy level offsets for efficient charge injection without requiring additional manufacturing steps.
2Reliability
If low-molecular materials are used in red and green light-emitting layers to achieve high light emission efficiency and long lifetime, then light emission efficiency and lifetime are improved, but interface properties with the common blue light-emitting layer deteriorate
Solution Approach 1:
The hole injection/transport layers and electron injection/transport layers serve as intermediary layers that bridge the interface between the low-molecular material red/green light-emitting layers and the blue light-emitting layer. These intermediary layers have energy levels that match both adjacent layers, enabling efficient charge transfer while maintaining the advantages of low-molecular materials in the red and green emitting layers.
3Ease of manufacture
If a common blue light-emitting layer is used over red and green layers to simplify manufacturing, then ease of manufacture is improved, but the intrinsic properties of red and green light-emitting layers are not sufficiently obtained
Solution Approach 1:
The injection/transport layers act as intermediary layers that enable the common blue light-emitting layer to effectively interact with the red and green light-emitting layers underneath. These intermediary layers ensure that charges injected from the blue layer can be efficiently transported to and recombine in the red and green layers, allowing the red and green layers to exhibit their intrinsic light-emitting properties despite being covered by the common blue layer.
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 enhances the light emission efficiency and extends the lifetime of the color organic EL display by improving hole or electron injection efficiency from the blue light-emitting layer to the red and green light-emitting layers, thereby achieving higher performance for the red and green organic EL elements.
Implementation Method 1
an organic EL display emitting light with use of an organic EL effect
Data Source
AI summary
An organic EL display includes: lower electrodes arranged on a substrate so as to correspond to red, green and blue organic EL elements, respectively; hole injection/transport layers arranged on the lower electrodes so as to correspond to the red, green and blue organic EL elements, respectively, the hole injection/transport layers having one or both of hole injection and hole transport properties; red and green organic light-emitting layers arranged on the hole injection/transport layers for the red and green organic EL elements, respectively, and including a low-molecular material; a blue organic light-emitting layer arranged on whole surfaces of the red and green organic light-emitting layers and the hole injection/transport layer for the blue organic EL element; and an electron injection/transport layer and an upper electrode arranged on a whole surface of the blue light-emitting layer, the electron injection/transport layer having one or both of electron injection properties and electron transport properties.