Thick-ETL OLEDs with Sub-ITO Grids for Outcoupling
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Solution Overview
Problem
Conventional OLEDs suffer from low out-coupling efficiency due to light being trapped in waveguide modes within the high refractive index organic and ITO layers, leading to significant loss through material absorption.
Innovation Solution
Incorporating a transparent grid layer with a refractive index less than or equal to the substrate, combined with an electron transport layer of increased thickness, to refract high-angle modes towards the substrate normal, enhancing out-coupling efficiency. The grid layer is patterned with dielectric materials like TiO2 and features space-filling polyhedra or voids, and the electron transport layer is thickened to minimize surface plasma modes and maximize waveguide power extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a transparent grid layer with low refractive index is incorporated, then out-coupling efficiency is improved, but device complexity increases
Solution Approach 1:
A transparent grid layer made of dielectric material (such as TiO2) with refractive index less than or equal to the substrate is introduced as an intermediary component between the substrate and the OLED. This grid layer acts as a mediator to refract high-angle waveguide modes toward the substrate normal, enabling efficient light extraction without requiring complex structural modifications to the OLED itself.
Solution Approach 2:
The refractive index parameter of the grid layer is specifically selected to be less than or equal to the substrate refractive index (n ≤ nsubstrate), creating an optimal optical parameter configuration that enables effective refraction of waveguide modes while maintaining compatibility with the substrate. This parameter optimization resolves the contradiction by achieving improved out-coupling through controlled refractive index matching.
2Loss of energy
If the electron transport layer thickness is increased, then waveguide power extraction is maximized, but manufacturing complexity increases
Solution Approach 1:
The thickness of the electron transport layer is increased to a specific range (50-200 nm, preferably 100-200 nm) to optimize waveguide power extraction. This parameter modification minimizes surface plasma modes and maximizes the coupling of waveguide modes to the substrate, achieving improved light extraction through controlled layer thickness rather than complex structural changes.
3Ease of manufacture
If conventional OLED structure is used, then manufacturing is simpler, but light extraction efficiency is poor due to waveguide mode trapping
Solution Approach 1:
The solution segments the light extraction function from the OLED structure itself by introducing a separate transparent grid layer. This segmentation allows the OLED to maintain its conventional simple structure for ease of manufacture, while the dedicated grid layer handles the complex optical function of extracting waveguide modes, thus resolving the contradiction between manufacturing simplicity and light 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 configuration increases substrate quantum efficiency by at least 40% and external quantum efficiency by at least 30%, significantly improving light extraction efficiency compared to conventional OLEDs.
Implementation Method 1
Incorporating a transparent grid layer with a refractive index less than or equal to the substrate, combined with an electron transport layer of increased thickness, to refract high-angle modes towards the substrate normal, enhancing out-coupling efficiency
Data Source
AI summary
An organic light emitting device is described. In certain embodiments, the device has a transparent substrate, a transparent grid layer disposed over the substrate, and an OLED disposed over the grid layer. The OLED can include an anode, a cathode, and at least one organic layer between the anode and cathode. A refractive index of the transparent grid layer is less than or equal to a refractive index of the transparent substrate. In certain embodiments, the at least one organic layer includes an electron transport layer having a thickness of at least 50 nm. In certain embodiments, the refractive index of the transparent grid layer is less than n=1.20, or in certain embodiments, less than n=1.05. Methods of manufacturing an organic light emitting device are also described.