OLED Emission Layer Structure for Charge-Balanced Light Emission
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Solution Overview
Problem
Existing organic electroluminescence display devices face challenges in achieving high luminous efficiency and long service life in light emitting elements.
Innovation Solution
A light emitting element design featuring a first electrode, a second electrode, and emission layers with specific host and dopant compositions, including a first emission layer with a first host and dopant, and a second emission layer with a hole transport host and electron transport host, where the first hole mobility is higher than the second, and electron mobility of the first host is significantly greater than the electron transport host, enhancing hole and electron mobility balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional emission layer structure is used, then the device structure is simple, but the luminous efficiency and service life are insufficient
Solution Approach 1:
The emission layer is divided into a first emission layer and a second emission layer with different host materials and charge transport characteristics. This segmentation allows each layer to be optimized for specific charge carrier transport, improving overall device reliability and service life while managing the complexity through functional specialization.
Solution Approach 2:
Different regions of the emission structure use different host materials with tailored properties. The first emission layer uses a host with specific hole and electron mobility characteristics, while the second emission layer uses a different host material. This local quality differentiation ensures optimal charge balance and recombination in each region, enhancing device performance and longevity.
2Use of energy by moving object
If charge carrier mobility is not balanced, then the device structure is simple, but the luminous efficiency is reduced
Solution Approach 1:
The patent systematically adjusts critical parameters including hole mobility (5.0×10^-6 to 1.0×10^-3 cm²/Vs), electron mobility (1.0×10^-5 to 1.0×10^-2 cm²/Vs), and LUMO energy levels (2.0 to 3.5 eV) of host materials. These parameter changes enable precise control of charge carrier balance and recombination efficiency, maximizing luminous efficiency while managing material selection complexity.
Solution Approach 2:
The emission layers employ composite material systems with specific host-dopant combinations. The first emission layer combines a host material with a first dopant, while the second emission layer uses a different host with a second dopant. This composite approach enables tailored charge transport and energy level alignment, improving luminous efficiency through optimized charge balance.
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 design improves luminous efficiency and extends the service life of the light emitting element by ensuring uniform distribution of holes and electrons, resulting in improved performance characteristics.
Implementation Method 1
a first hole mobility of the first host is in a range of about 5.0×10−6 cm2/Vs to about 1.0×10−3 cm2/Vs, a second hole mobility of a host mixture including the hole transport host and the electron transport host is in a range of about 1.0×10−6 cm2/Vs to about 1.0×10−4 cm2/Vs, and the first hole mobility is larger than the second hole mobility
Implementation Method 2
The organic electroluminescence display device includes so-called a self-luminescent light emitting element in which holes and electrons injected from a first electrode and a second electrode combine in an emission layer, and thus a luminescent material of the emission layer emits light
Data Source
AI summary
A light emitting element includes a first electrode, a second electrode disposed on the first electrode, and an emission part disposed between the first electrode and the second electrode and including a first emission layer and a second emission layer disposed on the first emission layer, the first emission layer may include a first host, and a first dopant, and the second emission layer may include a hole transport host different from the first host, an electron transport host, and a second dopant. A first hole mobility of the first host may be in a range of about 5.0×10−6 cm2/Vs to about 1.0×10−3 cm2/Vs, a second hole mobility of a host mixture including the hole transport host and the electron transport host may be in a range of about 1.0×10−6 cm2/Vs to about 1.0×10−4 cm2/Vs, and the first hole mobility may be larger than the second hole mobility.