Chiral OLED Structure for Circular Polarization at Lower Drive Voltage
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Solution Overview
Problem
Existing OLED devices face a tradeoff between light polarization and voltage difference, with thicker layers requiring higher drive voltages due to low charge carrier mobilities, and there is a need for displays that provide depth of focus information.
Innovation Solution
A chiral OLED device structure is developed with a helical photonic crystal structure that aligns light-emitting molecules in the plane of the device, using a layer-by-layer fabrication process with chiral liquid crystalline materials to achieve efficient circularly polarized light emission and allow for spontaneous emission into a wider cone of angles, incorporating ambipolar host materials for balanced electron and hole injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness of the chiral liquid crystalline layer is increased to improve light polarization efficiency, then the degree of circular polarization is improved, but the drive voltage increases due to low charge carrier mobilities
Solution Approach 1:
The patent modifies the molecular structure of the liquid crystalline materials to achieve a higher refractive index ratio between the extraordinary and ordinary rays. This parameter change allows the formation of a photonic stop band with a thinner layer, thereby maintaining high circular polarization efficiency while reducing the drive voltage requirement due to lower charge carrier mobility demands in thinner layers.
2Manufacturing precision
If the thickness of the chiral liquid crystalline layer is increased to form a fully developed reflection band, then the spectral width of the stop band is improved, but the drive voltage increases
Solution Approach 1:
By changing the refractive index ratio parameter of the liquid crystalline material, the patent achieves a photonic stop band with adequate spectral width in a thinner layer. This allows the reflection band to be fully formed with higher spectral quality factor without requiring increased layer thickness, thus avoiding the voltage penalty associated with thicker layers.
3Manufacturing precision
If the chiral liquid crystalline structure is optimized for high circular polarization, then the polarization purity is improved, but the angular emission range is narrowed
Solution Approach 1:
The patent adjusts the refractive index ratio parameter to optimize the photonic crystal properties, achieving a balance between circular polarization purity and angular emission range. This parameter optimization allows the device to maintain high polarization purity while expanding the angular emission range, making the display more versatile for different viewing conditions.
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 device achieves high energy efficiency with circularly polarized light emission, supports wider emission angles, and enables displays with depth of focus information, reducing the need for additional components like rear polarizers and improving display performance.
Implementation Method 1
The chiral structure acts as a photonic crystal for one of the circular polarizations of light produced by the OLED emitter
Implementation Method 2
one of the circular polarizations of light produced by the OLED emitter
Implementation Method 3
nearly all the light emitted is produced by stimulated emission into the band edge modes
Implementation Method 4
the light emitted into these modes is trapped in the photonic crystal structure. The presence of this trapped light stimulates further light emission
Data Source
AI summary
Disclosed herein are light emitting device that emit highly circularly polarized light. These devices may be used to form a dot-matrix display or an electronic information display comprised of a series of photopolymerizable, chiral liquid crystalline layers that can be solvent cast on a substrate. The mixture of chiral materials in each successive layer may be blended in such a way that each layer has the same chiral pitch and may also be blended so that the ordinary and extraordinary refractive indices in each layer match the other layers such that the complete assembly of layers will optically function as a single relatively thick layer or chiral liquid crystal. The chiral nematic material in each layer can spontaneously adopt a helical structure with a helical pitch. Further disclosed are pixel structures that not only emit light with brightness and chromaticity information, but also depth of focus information as well.