Four-Layer White OLED Device with Tandem Structure
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Solution Overview
Problem
Current OLED technologies face challenges in achieving broadband emission with strong intensity in the red, green, and blue portions of the spectrum while maintaining efficiency and stability, often requiring complex structures that increase drive voltage and reduce color gamut.
Innovation Solution
A white light-emitting OLED device with four light-emitting layers, including red, yellow, green, and blue layers, arranged in an energetically favorable order to achieve broadband emission with improved efficiency and stability, and a tandem structure with two white light-emitting units to enhance radiance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single light-emitting layer with multiple dopants is used to achieve broadband emission, then manufacturing complexity increases due to difficult dopant concentration control, but device structure is simplified
Solution Approach 1:
The patent divides the light-emitting function into multiple separate light-emitting layers, each containing a single type of luminescent dopant. This segmentation allows independent control of dopant concentrations in each layer, eliminating the manufacturing difficulties associated with controlling multiple dopant concentrations in a single layer while achieving broadband emission through the combination of emissions from all layers.
2Reliability
If two or more light-emitting layers are used to improve color and luminance efficiency, then stability increases, but achieving strong emission intensity in red, green, and blue portions becomes difficult
Solution Approach 1:
The patent optimizes each light-emitting layer individually with specific dopant concentrations tailored to maximize emission in particular spectral regions. The first layer is optimized for blue-green emission, the second for green-yellow emission, and the third for red emission. This local optimization of each layer's emission characteristics ensures strong overall emission intensity across all three primary color portions while maintaining the stability benefits of multiple layers.
3Illumination intensity
If a three-layer structure is used to provide three intensive emission peaks, then color emission improves, but luminance efficiency diminishes
Solution Approach 1:
The patent carefully controls the dopant concentration parameters in each light-emitting layer to optimize the balance between emission intensity and energy efficiency. By adjusting dopant concentrations within specific ranges (e.g., 0.1-5% for first layer, 0.1-10% for second layer, 0.1-5% for third layer), the patent achieves strong color emission while minimizing energy losses through optimized energy transfer from host to dopant molecules in each layer.
4Illumination intensity
If broadband emission is achieved through incomplete energy transfer from host to dopant, then white light emission is obtained, but manufacturing precision requirements increase
Solution Approach 1:
The patent segments the broadband emission requirement into multiple narrower emission bands from separate layers, each with complete or near-complete energy transfer. This eliminates the need to control incomplete energy transfer in a single layer, significantly reducing manufacturing precision requirements while still achieving the desired broadband white light emission through spectral combination.
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 four-layer structure provides improved color gamut, power efficiency, and lower voltage requirements, while the tandem structure increases radiance, addressing the limitations of previous OLED technologies.
Implementation Method 1
The organic EL unit includes at least a hole-transporting layer (HTL), a light-emitting layer (LEL), and an electron-transporting layer (ETL)
Implementation Method 2
A light-emitting layer having a host material and one or more luminescent dopant(s) can achieve light emission from both the host and the dopant(s) resulting in a broadband emission in the visible spectrum if the energy transfer from the host material to the dopant(s) is incomplete
Data Source
Figure 1
Figure 2a~2d
Figure 2e~2h
AI summary
A white light-emitting OLED device comprising: an anode and a cathode; at least four light-emitting layers provided between the anode and the cathode, wherein each of the four light-emitting layers produces a different emission spectrum when current passes between the anode and cathode, and such spectra combine to form white light; and wherein the four light-emitting layers include a red light-emitting layer, a yellow light-emitting layer, a blue light-emitting layer, and a green light-emitting layer, arranged such that: i) each of the light-emitting layers is in contact with at least one other light-emitting layer, ii) the blue light-emitting layer is in contact with the green light-emitting layer, and iii) the red light-emitting layer is in contact with only one other light-emitting layer.