White OLED Host Material Energy Level Gradient
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Solution Overview
Problem
Conventional white organic light emitting devices with single host and dopant in the light emitting layer suffer from electron and hole leakage, leading to reduced excitation efficiency and color stability under high luminance conditions.
Innovation Solution
A white organic light emitting device is designed with a charge generation layer between an anode and cathode, featuring a first and second light emitting layer stack where the first and second hosts have different transfer properties, with specific HOMO and LUMO levels, and a phosphorescent dopant with a maximum Photo Luminance peak in the 550 nm to 620 nm range, to enhance recombination efficiency and reduce driving voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single host and dopant are used in the light emitting layer, then the device structure is simple, but electron and hole leakage occurs leading to reduced excitation efficiency
Solution Approach 1:
The patent uses a composite host system comprising a first host material and a second host material with different energy levels. The first host has a higher HOMO level than the second host, creating an energy gradient that prevents charge carrier leakage while maintaining device simplicity. This composite approach resolves the contradiction by improving reliability through material composition rather than structural complexity.
2Ease of manufacture
If a single host and dopant configuration is used, then the manufacturing process is simple, but color stability deteriorates under high luminance conditions
Solution Approach 1:
The patent modifies the energy level parameters of the host materials to achieve color stability. By selecting a first host with a higher HOMO level and a second host with a lower HOMO level, the system maintains stable color emission under high luminance conditions while keeping the fabrication process simple. The energy level gradient prevents exciton dissociation and maintains color purity.
3Power
If the light emitting layer has a narrow energy band-gap, then the device can operate at lower voltages, but electron and hole leakage increases
Solution Approach 1:
The patent applies local quality by creating different energy level characteristics in different regions of the light emitting layer. The first host material provides regions with higher HOMO levels that prevent electron leakage, while the second host material provides regions with lower HOMO levels that facilitate hole injection. This spatial differentiation of energy levels allows low operating voltage while preventing charge carrier leakage.
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 achieves improved light emission efficiency, reduced driving voltage, and enhanced color stability under high luminance conditions by preventing exciton leakage and lowering the hole injection barrier, thereby maintaining efficiency and color accuracy.
Implementation Method 1
Each light emitting layer includes a single host and a dopant having the same color as light to be emitted, and is adapted to emit a corresponding color of light via recombination of electrons and holes introduced into the light emitting layer
Implementation Method 2
a phosphorescent dopant with a maximum Photo Luminance peak in the 550 nm to 620 nm range
Data Source
AI summary
A device for achieving reduced driving voltage and enhanced color stability under high luminance conditions includes an anode and cathode arranged on a substrate to be opposite each other, a charge generation layer between the anode and the cathode, a first stack formed between the anode and the charge generation layer and including a first light emitting layer, and a second stack formed between the charge generation layer and the cathode and including a second light emitting layer in which first and second hosts are doped with phosphorescent dopant, a HOMO level of the first host is greater than that of the second host, and a LUMO level of the first host is greater than an LUMO level of the second host.