OLED Emission Layer Composition for Charge Balance and Long Lifespan
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Solution Overview
Problem
Existing organic light-emitting devices face challenges in maintaining charge balance and longevity due to issues such as hole trapping and charge transfer delays, which affect the lifespan characteristics.
Innovation Solution
The device incorporates a specific composition of compounds in the emission layer and auxiliary layer, including a hole transporting host compound, an electron transporting host compound or bipolar host compound, a thermally activated delayed fluorescence (TADF) compound, and a fluorescent dopant, with the auxiliary layer containing two different compounds, and a controlled concentration of the dopant to ensure optimal charge balance and reduced spectral overlap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional organic light-emitting devices are used, then they can produce full-color images with wide viewing angles, but they suffer from hole trapping and charge transfer delays that reduce lifespan
Solution Approach 1:
The patent applies parameter changes by carefully controlling the concentration of the fluorescent dopant (fourth compound) to be equal to or less than 1/3 of the TADF compound (third compound) concentration, and by selecting compounds with specific energy level relationships (ΔEST ≤ 0.3 eV). These parameter optimizations minimize spectral overlap and reduce charge transfer delays, thereby extending device lifespan while maintaining full-color image production and wide viewing angles.
2Illumination intensity
If the concentration of fluorescent dopant is increased to enhance emission, then brightness improves, but spectral overlap increases causing charge transfer delays
Solution Approach 1:
The patent resolves this contradiction by optimizing the dopant concentration parameter to be equal to or less than 1/3 of the TADF compound concentration, and by selecting compounds where the distance between maximum peak wavelength of absorption spectrum and emission spectrum is equal to or less than 35 nm. This parameter optimization reduces spectral overlap and charge transfer delays while maintaining sufficient emission brightness for full-color display.
3Use of energy by moving object
If driving voltage is reduced to improve energy efficiency, then power consumption decreases, but charge balance becomes difficult to maintain
Solution Approach 1:
The patent employs composite materials by creating an emission layer containing four specific compounds: hole transporting host compound, electron transporting host compound or bipolar host compound, TADF compound with small singlet-triplet energy gap (ΔEST ≤ 0.3 eV), and fluorescent dopant. This composite structure enables efficient charge balance and low driving voltage operation by providing both hole and electron transport pathways while minimizing charge transfer delays through optimized compound interactions.
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 results in a low driving voltage and extended lifespan of the organic light-emitting device by maintaining charge balance and minimizing spectral overlap, thereby enhancing performance.
Implementation Method 1
the third compound may be a thermally activated delayed fluorescence (TADF) compound satisfying Equation 1 or an organometallic complex
Implementation Method 2
the fourth compound may be a fluorescent dopant
Data Source
AI summary
Provided are an organic light-emitting device and an apparatus including the same. The organic light-emitting device includes a first electrode, a second electrode, and an organic layer disposed between the first electrode and the second electrode. The organic layer includes an emission layer, a first region between the first electrode and the emission layer, a second region between the emission layer and the second electrode, and an auxiliary layer between the first region and the emission layer, and the emission layer includes a first compound, a second compound, a third compound, and a fourth compound. The organic light-emitting device exhibits a low driving voltage and a long lifespan.