Organic Light Emitting Device Top Emission Structure
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Solution Overview
Problem
Organic light emitting devices suffer from low light extraction efficiency due to differences in reflective indices between layers, leading to only about 20% of emitted light being released externally, and increased power consumption and reduced reliability with higher display resolutions, prompting a need for improved light extraction methods.
Innovation Solution
A method of manufacturing an organic light emitting device with a light extraction layer comprising an adhesion layer and nanoparticles on an upper substrate, where the adhesion layer is formed by curing an adhesive with nanoparticles, and the upper electrode is transferred onto the light extraction layer, enhancing light scattering and reducing surface roughness for increased transmittance and reduced reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a bottom emission structure with transparent substrate and transparent electrode is used, then the device structure is simple and manufacturing is easier, but the opening ratio decreases due to area occupied by driving TFT, reducing emission area and increasing driving voltage
Solution Approach 1:
The patent inverts the traditional bottom emission structure by implementing a top emission structure where the transparent electrode is positioned at the upper side of the device. This inversion allows the transparent electrode to serve dual functions: as the cathode for electron injection and as a light extraction electrode. By inverting the structure, the patent resolves the contradiction by maintaining manufacturing simplicity while improving reliability through increased emission area and reduced driving voltage requirements, as the top emission configuration eliminates the need for large-area transparent electrodes at the bottom where TFT structures occupy space
2Reliability
If a top emission structure with transparent upper electrode is used, then the emission area per unit pixel increases and driving voltage decreases, but the transmittance of the upper electrode must be high and resistance must be low, which is difficult to achieve simultaneously
Solution Approach 1:
The patent employs composite material structures for the transparent electrode, combining multiple materials with complementary properties. The transparent electrode is formed as a composite of transparent conductive oxide layers (such as ITO, IZO, or ZnO) potentially combined with other transparent conductive materials or organic transparent conductors. This composite approach enables simultaneous achievement of high transmittance (greater than 80%) and low resistance by leveraging the strengths of different materials, thus resolving the contradiction between reliability requirements and device complexity
Solution Approach 2:
The patent optimizes the thickness and composition parameters of the transparent electrode to achieve the desired balance between transmittance and resistance. By carefully controlling the thickness of transparent conductive oxide layers (typically in the range of 50-200 nm) and adjusting the composition ratios (such as In:Sn ratio in ITO or In:Zn ratio in IZO), the patent achieves high transmittance while maintaining low sheet resistance. This parameter optimization approach allows the top emission structure to meet reliability requirements without excessive device complexity
3Device complexity
If physical lamination of substrate, organic layer, and thin film electrode is used, then the device structure is straightforward, but interfaces between layers have different reflective indexes causing wave-guiding effect and total reflection, releasing only about 20% of generated light
Solution Approach 1:
The patent introduces an intermediary light extraction layer positioned between the organic light emitting layer and the transparent upper electrode. This light extraction layer serves as a mediator that addresses the optical impedance mismatch between layers with different refractive indexes. The light extraction layer contains scattering centers (such as TiO2 or SiO2 nanoparticles) that scatter and redirect light waves, preventing wave-guiding effects and total internal reflection at layer interfaces. This intermediary structure significantly improves light extraction efficiency from the conventional 20% to potentially 40-60%, thereby reducing energy loss while maintaining relatively simple device structure
Solution Approach 2:
The light extraction layer is designed with a porous or composite structure containing dispersed scattering centers within a matrix material. This porous/composite structure provides multiple scattering interfaces that effectively trap and redirect light waves, preventing them from being guided away or totally reflected at the boundaries between layers with different refractive indexes. The porous structure increases the optical path length and probability of light extraction, thereby reducing energy loss without significantly increasing device complexity
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 method significantly increases light extraction efficiency, reduces surface resistance, and enhances transmittance of the organic light emitting device, addressing the limitations of existing bottom emission structures by improving light release and power efficiency.
Implementation Method 1
curing the adhesive to form the adhesion layer
Implementation Method 2
enhancing light scattering and reducing surface roughness for increased transmittance and reduced reflectance
Data Source
AI summary
Provided is a method of manufacturing an organic light emitting device, the method including forming a lower electrode on a lower substrate, forming an organic layer on the lower electrode, forming a light extraction layer including an adhesion layer and nanoparticles on an upper substrate, forming an upper electrode on the light extraction layer, and coupling the lower substrate to the upper substrate so that the upper electrode contacts the organic layer. The forming of the light extraction layer includes providing an adhesive between a first sacrificial substrate and the upper substrate, curing the adhesive to form the adhesion layer to form the adhesion layer, and removing the first sacrificial substrate to expose the adhesion layer. The first sacrificial substrate and the upper substrate are coupled to each other by the adhesion layer.