High-Refractive Index Encapsulant for LED Light Extraction
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Solution Overview
Problem
Current solid-state lighting devices, such as LEDs, suffer from low external quantum efficiency due to light-trapping caused by refractive index differences between the LED chip and encapsulant, limiting the extraction of photons and overall efficiency.
Innovation Solution
Incorporating semiconductor nanocrystals with a refractive index greater than 1.5 into a matrix material to form a high-refractive index encapsulant, which reduces Fresnel reflection and total internal reflection, thereby enhancing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional encapsulant with refractive index 1.5-1.7 is used, then the device structure is simple and easy to manufacture, but light extraction efficiency is limited to 30% due to Fresnel reflection and total internal reflection
Solution Approach 1:
The patent employs composite materials by incorporating semiconductor nanocrystals (such as ZnS, CdSe, PbS) into the encapsulant matrix. This composite structure combines the optical properties of nanocrystals with the mechanical properties of the encapsulant material, achieving a refractive index greater than 1.7 while maintaining ease of manufacture through conventional encapsulation processes.
Solution Approach 2:
The patent changes the refractive index parameter of the encapsulant by incorporating nanocrystals with specific refractive indices. By selecting nanocrystals with refractive indices greater than 1.7 and optimizing their concentration and size distribution, the encapsulant achieves enhanced light extraction efficiency while minimizing optical scattering losses.
2Loss of energy
If the refractive index difference between LED chip (2.48) and encapsulant (1.5-1.7) is large, then Fresnel reflection and total internal reflection increase, but using materials with higher refractive index increases optical scattering
Solution Approach 1:
The patent applies local quality by controlling the size distribution and spatial distribution of nanocrystals within the encapsulant. By optimizing nanocrystal size to be significantly smaller than the wavelength of emitted light and ensuring uniform distribution, the encapsulant achieves high refractive index locally without creating significant optical scattering centers.
Solution Approach 2:
The patent optimizes multiple parameters simultaneously: nanocrystal size (kept below wavelength/10), nanocrystal concentration (optimized to achieve target refractive index), and nanocrystal material composition (selected for refractive index greater than 1.7). This multi-parameter optimization achieves the balance between reducing Fresnel reflection and minimizing optical scattering.
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 high-refractive index material increases light extraction quantum efficiency by allowing more photons to escape, leading to improved brightness and efficiency of solid-state lighting devices, with minimal optical scattering and long operational lifetime.
Implementation Method 1
light-trapping due to Fresnel reflection and total internal reflection of photons generated within the LED at the chip-encapsulant interface
Implementation Method 2
light-trapping due to Fresnel reflection and total internal reflection of photons generated within the LED at the chip-encapsulant interface
Implementation Method 3
Both Fresnel reflection and total internal reflection are a result of the difference in refractive indices of the adjacent materials on each side of the chip-encapsulant interface
Data Source
AI summary
A high-refractive index material that includes semiconductor nanocrystal compositions. The high-refractive index material has at least one semiconductor nanocrystal composition incorporated in a matrix material and has a refractive index greater than 1.5. The semiconductor nanocrystal composition has a semiconductor nanocrystal core of a II-VI, III-V, or IV-VI semiconductor material. A method of making a high-refractive index material includes incorporating, at least one semiconductor nanocrystal composition in a matrix material. An application of a high-refractive index material includes incorporating at least one semiconductor nanocrystal composition in a matrix material to form the high-refractive index material and depositing the high-refractive index material on the surface of a lighting device.