High Refractive Index Glass for OLED Light Extraction
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Solution Overview
Problem
Conventional OLED devices face challenges due to the mismatch in refractive indices between glass substrates and transparent electrode films, leading to inefficient light extraction, and existing high refractive index glasses have low liquidus viscosity, making them unsuitable for forming thin, large-area sheets using float or down-draw methods, and are costly due to the use of rare metal oxides.
Innovation Solution
A high refractive index glass with a composition of 0 to 10% B2O3, 0.001 to 35% SrO, 0.001 to 30% ZrO2+TiO2, and 0 to 10% La2O3+Nb2O5, with specific mass ratios and refractive indices, is developed to match the refractive indices of OLED components, enhancing devitrification resistance and allowing formation by float or down-draw methods while reducing rare metal oxide content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional glass substrate with refractive index of about 1.5 is used, then the glass can be easily formed into sheets, but the difference in refractive index between the glass substrate and the ITO film at their interface leads to a high reflectance, and hence light emitted from the organic light-emitting element cannot be extracted efficiently
Solution Approach 1:
The patent changes the refractive index parameter of the glass substrate from conventional values (about 1.5) to high refractive index values (1.8 or higher) by modifying the glass composition. This parameter change reduces the refractive index difference at the glass-ITO interface, thereby reducing reflectance and improving light extraction efficiency while maintaining formability through controlled composition ranges
2Loss of energy
If optical glass with high refractive index is used to improve light extraction efficiency, then the refractive index matches better with OLED components, but the glass has low liquidus viscosity, and hence the glass needs to be formed by a droplet forming method which is performed at a fast cooling rate because denitrification of glass occurs at the time of forming the glass otherwise
Solution Approach 1:
The patent creates a composite glass system combining multiple oxide components (SiO2, B2O3, Al2O3, La2O3, Nb2O5, Gd2O3, and other metal oxides) where each component contributes specific properties. The rare metal oxides (La2O3, Nb2O5, Gd2O3) provide high refractive index, while SiO2 and B2O3 maintain appropriate viscosity and formability, creating a composite material that achieves both high refractive index and ease of manufacturing
Solution Approach 2:
The patent carefully controls the composition parameters within specific ranges to achieve the desired balance. By limiting rare metal oxides to 0.1-10% total and adjusting the ratios of SiO2, B2O3, and other components, the glass achieves both high refractive index (1.8 or higher) and sufficient liquidus viscosity for conventional forming methods, eliminating the need for fast cooling rates
3Loss of energy
If rare metal oxides (La2O3, Nb2O5, Gd2O3) are added in the composition of glass to increase the refractive index, then the refractive index can be increased, but the material costs are high and the devitrification resistance of the glass lowers
Solution Approach 1:
The patent optimizes the concentration parameters of rare metal oxides within specific ranges (La2O3: 0-5%, Nb2O5: 0-5%, Gd2O3: 0-5%, with total 0.1-10%). This parameter optimization ensures sufficient refractive index enhancement while maintaining devitrification resistance. The patent also adjusts the ratios of other components (SiO2, B2O3, Al2O3) to compensate and maintain overall glass stability and resistance to devitrification
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 solution enables efficient light extraction by matching refractive indices, improves devitrification resistance, and reduces material costs by minimizing rare metal oxide usage, while allowing for the production of thin, large-area glass sheets suitable for OLED devices.
Implementation Method 1
a difference in refractive index between the glass substrate and the ITO film at their interface leads to a high reflectance
Implementation Method 2
This optical glass has a high refractive index nd but has a low liquidus viscosity, and hence the optical glass needs to be formed by, for example, a droplet forming method which is performed at a fast cooling rate, because denitrification of glass occurs at the time of forming the glass otherwise
Data Source
AI summary
Provided is a high refractive index glass, comprising, as a glass composition in terms of mass %, 0 to 10% of B2O2, 0.001 to 35% of SrO, 0.001 to 30% of ZrO2+TiO2, and 0 to 10% of La2O2+Nb2O5, having a mass ratio of BaO/SrO of 0 to 40 and a mass ratio of SiO2/SrO of 0.1 to 40, and having a refractive index nd of 1.55 to 2.3.