Grating-Structured Electrode for Broadband Light Extraction
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Solution Overview
Problem
Multi-layered surface light emitting devices, such as LEDs and OLEDs, suffer from significant light loss due to plasmon loss, where emitted light is coupled into surface plasmon polariton waves and absorbed by the metal electrode, particularly for broadband light sources like white OLEDs, with existing grating structures only effective for narrow wavelength ranges.
Innovation Solution
A light emitting device with a periodic grating structure on the metal electrode layer is engineered to inhibit the formation of surface plasmon polariton waves across the visible spectrum, using a deep-subwavelength grating period and optimized geometry to reduce coupling into surface plasmons, thereby enhancing light extraction efficiency for broadband light sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a periodic grating-structured electrode is used to reduce plasmon loss, then light extraction efficiency is improved for narrow wavelength ranges, but effectiveness is lost for broadband light sources
Solution Approach 1:
The patent applies parameter changes by using a deep-subwavelength grating period (λg ≤ 200 nm) that is much smaller than the wavelength of emitted light. This parameter change transforms the grating's interaction with light from wavelength-selective Bragg scattering to a broadband suppression mechanism that effectively reduces plasmon loss across the entire visible spectrum for broadband light sources like white OLEDs.
Solution Approach 2:
The patent introduces a new dimensional approach by placing the grating structure in the deep-subwavelength regime, effectively moving the operating regime to a different scale dimension. This deep-subwavelength dimension allows the grating to interact with all visible wavelengths simultaneously, providing broadband effectiveness rather than narrowband selectivity.
2Adaptability or versatility
If a deep-subwavelength grating period is used to achieve broadband effectiveness, then manufacturing precision requirements increase
Solution Approach 1:
The patent applies partial action by using a grating period that is excessively small (deep-subwavelength scale of ≤ 200 nm), much smaller than the wavelength of light. This excessive smallness ensures broadband effectiveness while the proximity to the emitting layer (≤ 100 nm separation) provides additional leverage to achieve the desired plasmon loss reduction without requiring extremely tight tolerances on the grating depth or exact period.
Solution Approach 2:
The patent introduces an intermediary approach by placing the grating-structured electrode in close proximity (at most 100 nm separation) to the emitting layer. This close positioning acts as an intermediary mechanism that enhances the grating's ability to suppress plasmon loss across broadband wavelengths while reducing the stringency of manufacturing precision requirements for the grating structure itself.
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 effectively reduces plasmonic loss across the entire visible spectrum, improving the operational efficiency of light emitting devices by minimizing energy absorption in the metal electrode, leading to increased light output and reduced energy consumption.
Implementation Method 1
Plasmon loss in light emitting devices may be reduced by using a periodic grating-structured electrode having a period that is comparable to the wavelength of the emitted light so as to induce Bragg scattering of the SPP wave into free light.
Implementation Method 2
SPP waves are surface waves confined to propagating along the interface between the metal electrode layer and the emitting material layer. Energy in the SPP waves is eventually absorbed by the metal electrode and thus leads to inefficient operation of the (O)LED.
Data Source
AI summary
A light emitting device includes a substrate layer, a first electrode layer, a light emitting layer, and a patterned second electrode layer. The patterned second electrode layer includes a periodic grating structure having a grating period λg less than or equal to 200 nm and the patterned second electrode layer and the light emitting layer are separated by at most 100 nm.