Inorganic Insulating Layer for OLED Electron Injection
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Solution Overview
Problem
Conventional organic light emitting devices face challenges with electron injecting efficiency due to large differences in work functions between the electron transporting layer and the cathode, leading to excessive hole injection, which lowers light emitting efficiency, as LiF lacks hole blocking ability.
Innovation Solution
Incorporating an inorganic insulating layer with a band gap of 3.3 eV or more and a band offset of 0.45 eV or less between the electron injecting electrode and the organic material layer, utilizing materials like Ta2O5 and Pb(Ti0.55Zr0.45)O3, to enhance electron injecting and hole blocking capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiF is used as the electron injecting layer material, then electron injecting ability is improved, but hole blocking ability is lost
Solution Approach 1:
The patent uses a composite structure combining LiF layer and Alq3 layer. The LiF layer provides excellent electron injecting ability by reducing the work function difference between cathode and electron transporting layer, while the Alq3 layer provides hole blocking ability to prevent holes from reaching the cathode. This composite material approach resolves the contradiction by integrating two materials with complementary functions.
2Device complexity
If there is a large difference in work functions between electron transporting layer and cathode, then device structure is simplified, but electron injecting efficiency decreases
Solution Approach 1:
The patent introduces LiF as an intermediary layer between the cathode and the electron transporting layer. This intermediate layer has a work function that is intermediate between the cathode and the electron transporting layer, creating gradual energy level transitions that facilitate electron injection while maintaining structural simplicity.
3Device complexity
If excessive holes are injected toward the cathode, then device structure is simplified, but light emitting efficiency decreases
Solution Approach 1:
The Alq3 layer serves as an intermediary that selectively blocks holes from reaching the cathode while allowing electrons to pass through. This prevents excessive hole injection that would otherwise reduce light emitting efficiency, while maintaining the overall simplicity of the device structure through the use of just two functional layers.
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 significantly improves electron injecting and hole blocking effects, resulting in enhanced efficiency, luminance, and extended lifetime of the organic light emitting device, without the need for additional hole blocking layers.
Implementation Method 1
an inorganic insulating layer formed from the materials having a band gap of 3.3 eV or more
Implementation Method 2
a band offset of 0.45 eV or less
Implementation Method 3
excellent electron injecting and hole blocking abilities
Data Source
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AI summary
The present invention provides an organic light emitting device, wherein an electron injecting electrode, at least one organic material layer including a light emitting layer, and a hole injecting electrode are laminated; and an inorganic insulating layer formed from the materials having a band gap of 3.3 eV or more, and a band offset of 0.45 eV or less, is provided between the electron injecting electrode and the organic material layer; and a method for preparing the same.