Stacked Light-Emitting Element with Charge Generation Layer
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Solution Overview
Problem
Blue phosphorescent substances in light-emitting elements have significantly shorter lifetimes compared to red and green phosphorescent substances, limiting the practical use of multicolor and white light-emitting elements with high emission efficiency.
Innovation Solution
A light-emitting element structure incorporating a stack of two or more light-emitting units with a charge generation layer in between, where each unit contains two kinds of phosphorescent substances, one with an emission maximum in the 400-500 nm range and the other in the 500-700 nm range, allowing for integrated blue light emission with reduced load on the blue phosphorescent substance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If blue phosphorescent substances are used to achieve high emission efficiency in multicolor and white light-emitting elements, then emission efficiency is improved, but lifetime is significantly reduced
Solution Approach 1:
The patent divides the light-emitting element into multiple light-emitting units stacked in the thickness direction. Each unit contains phosphorescent substances emitting in different wavelength ranges (blue: 400-500nm, green: 500-560nm, red: 600-700nm). By segmenting the emission function across multiple units, the blue phosphorescent substance in each unit operates at reduced load, extending its lifetime while maintaining high overall emission efficiency through the cumulative output of all units.
2Device complexity
If a single light-emitting unit with blue phosphorescent substance is used, then device structure is simple, but lifetime is short due to high load on blue phosphorescent substance
Solution Approach 1:
The patent segments the high-load operation into multiple low-load units. Each unit has a simplified structure containing phosphorescent substances, and multiple units are stacked to achieve the desired emission intensity. This segmentation allows each blue phosphorescent substance to operate under reduced stress, extending lifetime while the overall multi-unit structure maintains relative simplicity.
Solution Approach 2:
The patent transitions from a single planar light-emitting layer to a three-dimensional stacked structure of multiple light-emitting units in the thickness direction. This dimensional change allows the system to distribute the emission load vertically across multiple units, reducing the burden on blue phosphorescent substances in each unit while maintaining a compact overall structure.
3Duration of action of stationary object
If multiple light-emitting units are stacked to reduce load on blue phosphorescent substance, then lifetime is extended, but device complexity increases
Solution Approach 1:
The patent uses segmentation to divide the light-emitting function into multiple standardized units. Each unit has a relatively simple structure with phosphorescent substances in specific wavelength ranges. By stacking these modular units, the system achieves extended lifetime through reduced individual unit load while managing complexity through standardization and modularity.
Solution Approach 2:
Each light-emitting unit in the stack serves multiple functions: it provides emission in its specific wavelength range, contributes to overall emission intensity, and operates at reduced load to extend lifetime. This multi-functionality of each unit justifies the stacked structure, as each component performs several roles that reduce the need for additional specialized elements.
4Productivity
If blue phosphorescent substance operates at high intensity, then white light emission efficiency is high, but color rendering properties deteriorate
Solution Approach 1:
The patent segments the white light emission function into multiple units, each emitting in different wavelength ranges (blue, green, red). By distributing the emission load across these segmented units, each phosphorescent substance operates at lower intensity, maintaining stable emission characteristics and color rendering properties while achieving high overall white light emission efficiency through the combined output.
Solution Approach 2:
The patent applies local quality by assigning specific wavelength range emission functions to different light-emitting units. Each unit is optimized for its specific wavelength range with appropriate phosphorescent substances, allowing each local region (unit) to maintain optimal emission quality and color rendering while contributing to the overall white light output.
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 extends the lifetime of blue phosphorescent substances and the entire light-emitting element, achieving high reliability and efficient white light emission with improved color rendering properties.
Implementation Method 1
light emission from the triplet excited state (T*) is referred to as phosphorescence. The statistical generation ratio of the excited states in the light-emitting element is considered to be S*:T*=1:3. Therefore, a light-emitting element including a phosphorescent compound capable of converting the triplet excited state into light emission has been actively developed in recent years.
Implementation Method 2
application of a voltage between the pair of electrodes causes injection of electrons from the cathode and holes from the anode into the EL layer, and thus a current flows. By recombination of the injected electrons and holes, the organic compound having a light-emitting property is excited and provides light emission from the excited state.
Data Source
AI summary
Disclosed is a light-emitting element comprising a plurality of light-emitting units which are separated from one another by a charge generation layer. The light-emitting units each have a light-emitting layer which is featured by a stack of two layers. Each of the two layers includes a host material and a phosphorescent material where the phosphorescent material in one of the two layers is blue emissive while the phosphorescent material in the other of the two layers exhibits a maximum emission peak in a range from 500 nm to 700 nm. The phosphorescent material exhibiting a maximum emission peak in a range from 500 nm to 700 nm may be different from light-emitting unit to light-emitting unit. An additive may be included in at least one of the two layers so that an exciplex is formed with the host material.