Photoluminescent LCD Phase Difference Layers for Contrast Ratio
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Solution Overview
Problem
Photoluminescent liquid crystal displays (LCDs) face challenges with low contrast ratio and deteriorated display characteristics due to scattering characteristics of light emitting elements, which are not effectively addressed by conventional structures.
Innovation Solution
The implementation of a photoluminescent LCD with specific refractive index conditions for upper and lower phase difference layers, combined with a color conversion layer using light emitting elements like quantum dots or phosphors, to enhance contrast ratio and display characteristics by controlling light leakage in black mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a photoluminescent LCD uses a conventional structure with a polarizer on the light emitting element, then the structure is simple, but the contrast ratio is low and display characteristics are deteriorated due to light scattering
Solution Approach 1:
The patent divides the phase difference compensation into multiple layers: a lower phase difference layer with negative uniaxial anisotropy and an upper phase difference layer with positive uniaxial anisotropy. This segmentation allows each layer to compensate for different aspects of light scattering, thereby improving contrast ratio while maintaining structural feasibility
Solution Approach 2:
The patent uses composite optical structures combining different material properties: the lower phase difference layer uses materials with negative uniaxial anisotropy (nx<ny=nz) while the upper layer uses materials with positive uniaxial anisotropy (nx>ny=nz). This composite approach enables effective compensation of scattering effects from light emitting elements
2Device complexity
If a color filter is used to display color, then the structure is conventional and simple, but light absorption is substantial and photoefficiency is lowered
Solution Approach 1:
The patent changes the optical parameters of the phase difference layers by controlling their refractive index relationships (nx<ny=nz for lower layer, nx>nymz for upper layer) and thickness direction retardations. This allows the system to achieve color display and scattering compensation without using light-absorbing color filters, thereby maintaining high photoefficiency
3Illumination intensity
If the upper phase difference layer has specific refractive index relationships (nx1≥nymz1) and thickness direction retardation, then light leakage is reduced and contrast ratio is improved, but the manufacturing precision requirements are increased
Solution Approach 1:
The patent specifies precise parameter ranges for the upper phase difference layer: refractive indexes satisfying nx1≥nymz1 and thickness direction retardation Rth1 within (−0.6×Rth,cell+60)×navg−210 to (−0.6×Rth,cell+260)×navg−420. These parameter specifications enable effective light leakage reduction while providing clear manufacturing guidelines
Solution Approach 2:
The patent establishes a feedback relationship between the liquid crystal layer's thickness direction retardation (Rth,cell) and the upper phase difference layer's retardation (Rth1) through the formulaic range specification. This allows the upper layer parameters to be adjusted based on the liquid crystal layer characteristics, optimizing performance while accommodating manufacturing variations
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 maintains low black luminance in all directions, thereby increasing the contrast ratio and improving display characteristics by effectively reducing light leakage and enhancing viewing angle performance.
Implementation Method 1
an upper phase difference layer between the liquid crystal layer and the upper polarization layer and having refractive indexes satisfying the following inequation: nx1≥nymz1 (where nx1 denotes a refractive index of the upper phase difference layer at a slow axis thereof, ny1 denotes a refractive index of the upper phase difference layer at a fast axis thereof, and nz1 denotes a refractive index in a direction perpendicular to the slow axis and the fast axis thereof)
Implementation Method 2
research on a photoluminescent liquid crystal display (LCD) that displays a color by using a light emitting element instead of a color filter has been made
Data Source
AI summary
A liquid crystal display includes a light source, lower and upper substrates facing each other and on the light source, a liquid crystal layer between the lower and upper substrates, an upper polarization layer between the upper substrate and the liquid crystal layer, an upper phase difference layer between the liquid crystal layer and the upper polarization layer and having refractive indexes satisfying the following inequation: nx1≥ny1>nz1, a lower polarization layer disposed between the light source and the lower substrate, and a lower phase difference layer disposed between the light source and the lower substrate and having refractive indexes satisfying the following inequation: nx2>ny2 and nx2>nz2, where a thickness direction retardation of the upper phase difference layer satisfies the following inequation:(−0.6×Rth,cell+60)×navg−210≤Rth1≤(−0.6×Rth,cell+260)×navg−420.