OLED Light-Emitting Element With Asymmetric Host LUMO Levels
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Solution Overview
Problem
Organic light-emitting diodes (OLEDs) face significant luminance degradation over time, limiting their lifetime and reliability, especially when used in lighting applications, where they need to match or exceed the lifespan of traditional LED lamps.
Innovation Solution
A light-emitting element structure featuring multiple layers with specific host materials and emission center substances, where the LUMO level of the host material on the anode side is higher than on the cathode side, dispersing the recombination region and reducing degradation by creating a barrier for electron transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a single light-emitting layer is used in OLED, then the device structure is simple, but luminance degradation occurs rapidly reducing lifetime
Solution Approach 1:
The light-emitting layer is divided into multiple sub-layers (first light-emitting layer with hole-transporting host material and second light-emitting layer with electron-transporting host material) to disperse the recombination region. This segmentation prevents concentration of stress and degradation at a single interface, thereby extending device lifetime while maintaining a relatively straightforward layered structure.
2Reliability
If the recombination region is concentrated at one interface, then the element structure is simple, but degradation is severe reducing reliability
Solution Approach 1:
Different host materials with complementary transport properties are used in different regions of the light-emitting layer. The first light-emitting layer uses a hole-transporting host material while the second uses an electron-transporting host material, creating local optimization of charge transport and dispersing the recombination region to improve luminance stability.
3Duration of action of stationary object
If electron transport is unrestricted, then the device operation is efficient, but degradation accelerates reducing lifetime
Solution Approach 1:
The second light-emitting layer with electron-transporting host material acts as an intermediary region that facilitates controlled electron transport. This layer mediates between the electron-injecting cathode and the recombination zone, enabling efficient electron injection while distributing electron flow to prevent excessive degradation at any single location.
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 structure significantly extends the lifetime of OLEDs by minimizing luminance degradation, ensuring high reliability and performance over time, making them suitable for both display and lighting applications.
Implementation Method 1
In a basic structure of such a light-emitting element, a layer containing a light-emitting substance is interposed between a pair of electrodes. By applying voltage to this element, light emission from the light-emitting substance can be obtained.
Data Source
AI summary
Provided is a light-emitting element with a small degree of luminance degradation with accumulation of driving time (a long-lifetime light-emitting element). Provided is a light-emitting element in which a light-emitting layer with an electron-transport property is formed with a plurality of layers containing different host materials. Further, the LUMO level of a host material on an anode side is higher than the LUMO level of a host material on a cathode side. With such a structure, it is possible to provide a long-lifetime light-emitting element with little degradation in luminance with accumulation of driving time.