Organic EL Display Element Low Refractive Index Layer
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Solution Overview
Problem
Existing organic electroluminescence (EL) elements face challenges in improving light extraction efficiency and reducing power consumption, particularly due to insufficient carrier injection and increased drive voltage when using first order optical interference, which leads to increased power consumption and decreased light extraction efficiency.
Innovation Solution
Incorporating a low refractive index layer in contact with a light transmissive cathode, where the cathode serves as a reflective surface of an optical resonator, allowing for optimized optical resonator size and film thickness of the light emitting and functional layers, thereby reducing power consumption and increasing light extraction efficiency without excessive film thickness increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If film thickness of the light emitting layer and functional layer is increased to utilize first order optical interference, then light extraction efficiency is improved, but drive voltage increases and power consumption increases
Solution Approach 1:
A low refractive index layer is introduced as an intermediary between the cathode and the light emitting layer. This layer has a refractive index lower than both the cathode and the light emitting layer, creating favorable optical conditions for first order interference without requiring excessive thickness of the light emitting or functional layers. The low refractive index layer acts as an optical mediator that enhances light extraction efficiency while maintaining acceptable drive voltage and power consumption levels.
Solution Approach 2:
The refractive index parameter of the layer adjacent to the light emitting layer is changed by introducing a low refractive index layer. This parameter change creates the necessary optical conditions for first order interference to occur at reasonable film thicknesses, thereby improving light extraction efficiency without the penalty of increased drive voltage and power consumption that would result from simply thickening the light emitting or functional layers.
2Ease of manufacture
If film thickness of the functional layer is increased to optimize optical resonator size, then light extraction efficiency is improved, but attenuation of light between the light emitting layer and cathode increases
Solution Approach 1:
The low refractive index layer serves as an optical intermediary that reduces light attenuation between the light emitting layer and the cathode. By providing a layer with lower refractive index than both adjacent layers, it creates favorable optical conditions that minimize reflection and maximize light transmission, thereby reducing energy loss while still enabling effective light extraction through first order interference.
Solution Approach 2:
The refractive index parameter of the interface between the light emitting layer and the cathode is modified by inserting the low refractive index layer. This parameter change optimizes the optical path and reduces light attenuation, allowing the functional layer to maintain an optimal thickness for optical resonator formation without suffering from excessive light absorption or reflection losses.
3Ease of manufacture
If distance between the light emitting layer and low refractive index layer is increased to utilize first order optical interference, then light extraction efficiency is improved, but drive voltage increases
Solution Approach 1:
The low refractive index layer acts as an optical mediator that enables first order interference to occur at a moderate distance from the light emitting layer. This intermediary layer creates the necessary optical path difference for constructive interference without requiring such a large increase in distance that would otherwise be needed, thereby maintaining drive voltage at acceptable levels while still achieving improved light extraction efficiency.
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 light extraction efficiency and reduces power consumption by utilizing first order optical interference without increasing the film thickness of the light emitting and functional layers, leading to a decrease in drive voltage and improved light extraction.
Implementation Method 1
first order optical interference can be used without excessively increasing film thickness for the light emitting layer and the functional layer
Implementation Method 2
a low refractive index layer-side of the cathode becomes a reflective surface of an optical resonator
Data Source
AI summary
An organic EL element includes an anode, a light emitting layer, a functional layer, a cathode, and a low refractive index layer. The light emitting layer is disposed above the anode. The functional layer is disposed on and in contact with the light emitting layer and includes a first metal. The cathode is disposed on and in contact with the functional layer and is made of a light transmissive metal oxide. The low refractive index layer is disposed on and in contact with the cathode. Refractive index of the low refractive index layer is smaller than refractive index of the cathode, film thickness of the functional layer is from 15 nm to 35 nm, and a distance between an anode-side surface of the light emitting layer and an interface between the cathode and the low refractive index layer is 110 nm or greater.