Three-Layer Organic EL Light-Emitting Structure for Blue Phosphorescence
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Solution Overview
Problem
Organic electroluminescence (EL) elements using blue phosphorescence-emitting materials require high voltage for driving due to low light-emitting efficiency, as the host materials needed to confine electrons and holes have wide gaps between Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO), hindering efficient electron and hole transport.
Innovation Solution
A three-layered light-emitting structure where the first and second host materials have specific HOMO and LUMO levels relative to the organic light-emitting material, with a third host material having a large gap between HOMO and LUMO, ensuring electron holes and electrons are confined and recombine efficiently in the third layer, reducing voltage requirements and enhancing quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a host material with a wide gap between HOMO and LUMO is used to confine electrons and holes in the light-emitting layer, then the light-emitting efficiency is improved, but the electron and hole transport becomes inefficient
Solution Approach 1:
The light-emitting layer is divided into three sub-layers (first, second, and third light-emitting layers) with different host materials. The first and second host materials have smaller HOMO-LUMO gaps that facilitate efficient electron and hole transport, while the third host material has a larger gap that confines carriers for efficient recombination and light emission.
Solution Approach 2:
Different regions of the light-emitting layer are assigned different host materials with optimized properties. The first and second light-emitting layers use host materials optimized for carrier injection and transport, while the third light-emitting layer uses a host material optimized for carrier confinement and radiative recombination.
2Use of energy by moving object
If a phosphorescence-emitting material with 100% internal quantum efficiency is used, then the power consumption is reduced, but blue light emission requires higher energy and results in low light-emitting efficiency
Solution Approach 1:
The patent uses a composite structure combining phosphorescence-emitting material (for high internal quantum efficiency and low power consumption) with a three-layer host material system (for efficient carrier transport and confinement). This composite approach overcomes the limitation of blue phosphorescence-emitting materials by providing efficient transport pathways while maintaining carrier confinement for radiative recombination.
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 allows for efficient electron and hole transfer to the third light-emitting layer, increasing recombination ratios and internal quantum efficiency, thereby reducing the driving voltage and enhancing light-emitting efficiency.
Implementation Method 1
the organic light-emitting material is a phosphorescence-emitting material
Implementation Method 2
a voltage is applied across the cathode and the anode so that electron holes are injected from the cathode into the organic layer and electrons are injected from the anode to the organic layer. The electron holes and the electrons which have been injected from the electrodes recombine in the light-emitting layer to form an exciton.
Data Source
AI summary
An organic EL element (1) includes a three-layer-structured light-emitting layer (5). A first light-emitting layer (5a) is made of a host material higher in HOMO than an organic light-emitting material (|HOMO (host material for first light-emitting layer)|>|HOMO (phosphorescence-emitting material)|). A second light-emitting layer (5c) is made of a host material lower in LUMO than the organic light-emitting material (|LUMO (host material for second light-emitting layer) |<|LUMO (phosphorescence-emitting material)|). A third light-emitting layer (5b) is made of a material higher in HOMO and lower in LUMO than the organic light-emitting material (|HOMO (host material for third light-emitting layer)|>|HOMO (phosphorescence-emitting material)|, |LUMO (host material for third light-emitting layer)|<|LUMO (phosphorescence-emitting material)|). This ensures transferring holes and electrons to the third light-emitting layer (5c). Consequently, a recombination ratio between holes and electrons increases, a voltage for driving the organic EL element (1) decreases, and light-emitting efficiency increases.