OLED Hole-Transporting Layer HOMO Alignment for Efficiency
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Solution Overview
Problem
Conventional current-excitation light-emitting elements have short lifespans and low emission efficiency due to the lack of durability in their hole-blocking layers, leading to inefficient light emission.
Innovation Solution
A light-emitting element structure is developed with specific layer configurations, including a hole-injecting layer, hole-transporting layers, and a carrier control layer, where the highest occupied molecular orbital (HOMO) levels are strategically aligned to control the transport of holes and electrons, enhancing emission efficiency and extending the element's lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a hole-blocking layer is provided to improve light emission efficiency, then emission efficiency is improved, but durability deteriorates and element lifespan becomes extremely short
Solution Approach 1:
The invention extracts and removes the problematic hole-blocking layer from the conventional light-emitting element structure. By eliminating this layer that causes durability issues, the patent achieves both improved durability and maintained emission efficiency through the alternative structure of multiple hole-transporting layers with different HOMO levels
Solution Approach 2:
The invention segments the single hole-transporting layer into multiple distinct layers (first hole-transporting layer, second hole-transporting layer, and third hole-transporting layer) with progressively different HOMO levels. This segmentation allows each layer to perform specialized functions in controlling hole transport, achieving both efficiency and durability
2Ease of manufacture
If conventional layer structure is used, then manufacturing is simple, but emission efficiency is low
Solution Approach 1:
The invention applies local quality by giving each hole-transporting layer distinct properties through different HOMO levels. The first layer has one HOMO level, the second layer has a higher HOMO level, and the third layer has an even higher HOMO level, allowing precise local control of hole transport characteristics to maximize emission 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
The proposed structure reduces hole transport rates, increases recombination probability, and improves emission efficiency, resulting in a light-emitting element with higher efficiency and longer lifespan, which can be applied to devices for reduced power consumption.
Implementation Method 1
By applying voltage to a light-emitting element, electrons and holes are injected from a pair of electrodes into a layer which contains an organic compound having a light-emitting property, so that current flows therethrough. Then, by recombination of these carriers (electrons and holes), the organic compound having a light-emitting property forms an excited state, and emits light when the excited state returns to a ground state.
Implementation Method 2
Note that an excited state of an organic compound can be a singlet excited state or a triplet excited state, and luminescence from a singlet excited state is referred to as fluorescence
Implementation Method 3
luminescence from a triplet excited state is referred to as phosphorescence
Data Source
AI summary
In a light-emitting element including an EL layer between a pair of electrodes, between an electrode functioning as an anode and a fourth layer having a light-emitting property (light-emitting layer), the EL layer includes at least a first layer having a hole-injecting property (hole-injecting layer), a second layer having a hole-transporting property (first hole-transporting layer), and a third layer having a hole-transporting property (second hole-transporting layer). The absolute value of the highest occupied molecular orbital level (HOMO level) of the second layer is larger than the absolute value of the highest occupied molecular orbital level (HOMO level) of each of the first layer and the third layer. With such a structure, the rate of transport of holes injected from the electrode functioning as an anode is reduced and emission efficiency of the light-emitting element is improved.