Transparent Mirrorless LED Light Extraction
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Solution Overview
Problem
Conventional LEDs suffer from reduced efficiency due to re-absorption of reflected light by the emitting layer, as the reflected photons have energies similar to the band-gap energy, leading to decreased output power.
Innovation Solution
The development of an (Al, Ga, In)N light emitting diode (LED) that extracts light from multiple sides, including the top and bottom, by eliminating mirrors and using transparent layers and shaped optical elements to minimize internal reflections and enhance light extraction, with features such as textured surfaces and phosphor layers to increase light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If mirrors are used to reflect light back through the LED, then light output from the front side is increased, but light extraction efficiency decreases due to re-absorption by the emitting layer
Solution Approach 1:
The patent removes the mirror component from the LED structure entirely. By extracting the reflective element, the design eliminates the re-absorption problem that occurs when reflected light passes back through the emitting layer, thereby improving light extraction efficiency while maintaining front-side light output through alternative extraction paths.
Solution Approach 2:
The patent transitions from unidirectional light extraction (front side only) to multi-directional light extraction by enabling light to exit through both the front and back sides of the LED. This dimensional change in light extraction geometry allows the system to achieve high light output without requiring mirrors, as light can escape through multiple pathways simultaneously.
2Device complexity
If conventional single-side light extraction is used, then device structure is simple, but light extraction efficiency is limited
Solution Approach 1:
The patent adds a third dimension to light extraction by enabling light to exit through both the front and back surfaces of the LED chip. This multi-directional extraction approach doubles the effective extraction area without significantly complicating the device structure, as it primarily requires removing the back contact layer and allowing light to pass through the substrate.
Solution Approach 2:
The patent applies different optical properties to different regions of the LED structure. The front surface maintains its conventional reflective contact structure, while the back surface is modified to be transparent or partially transparent, creating local quality differences that enable multi-directional light extraction and improve overall extraction efficiency.
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 approach significantly increases light extraction efficiency and output power by minimizing re-absorption and allowing light to be emitted from multiple sides, resulting in improved LED performance.
Implementation Method 1
textured surfaces and phosphor layers to increase light extraction efficiency
Implementation Method 2
phosphor layers to increase light extraction efficiency
Data Source
AI summary
An (Al, Ga, In)N light emitting diode (LED) in which multi-directional light can be extracted from one or more surfaces of the LED before entering a shaped optical element and subsequently being extracted to air. In particular, the (Al, Ga, In)N and transparent contact layers (such as ITO or ZnO) are embedded in or combined with a shaped optical element, which may be an epoxy, glass, silicon or other material molded into a sphere or inverted cone shape, wherein most of the light entering the inverted cone shape lies within a critical angle and is extracted. The present invention also minimizes internal reflections within the LED by eliminating mirrors and/or mirrored surfaces, in order to minimize re-absorption of the LED's light by the emitting layer (or the active layer) of the LED. To assist in minimizing internal reflections, transparent electrodes, such as ITO or ZnO, may be used. Surface roughening by patterning or anisotropically etching (i.e., creating microcones) may also assist in light extraction, as well as minimizing internal reflections.