Porous Scattering Layer for OLED Outcoupling Efficiency
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Solution Overview
Problem
Thin-film organic light-emitting diodes (OLEDs) suffer from low outcoupling efficiency, with only 20 to 30% of emitted photons escaping the device, due to the planarity of the device and refractive indices of the thin-film stack, limiting the conversion of electrical power into optical power.
Innovation Solution
A scattering layer is introduced, comprising a substrate and a host medium with high refractive index and air voids, which redistributes light propagation, enhancing outcoupling efficiency by trapping and redirecting substrate-trapped light through a porous film structure fabricated using scalable phase inversion processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a planar OLED structure is used, then device simplicity is maintained, but outcoupling efficiency remains low at only 20 to 30%
Solution Approach 1:
The patent applies porous materials by introducing a scattering layer containing air voids (porosity) into the OLED structure. The air voids create refractive index contrast that scatters light and traps substrate modes, converting them into extractable light. This resolves the contradiction by maintaining the simplicity of the planar device architecture while dramatically improving outcoupling efficiency to approximately 65% through the porous scattering layer.
Solution Approach 2:
The scattering layer is formed as a composite material combining a host medium (such as polyimide or PDMS) with dispersed air voids. This composite structure provides both mechanical integrity and optical scattering functionality, enabling the device to maintain structural simplicity while achieving enhanced light extraction through the composite's unique optical properties.
2Loss of energy
If a scattering layer with air voids is introduced, then outcoupling efficiency increases to approximately 65%, but device structure becomes more complex
Solution Approach 1:
The scattering layer is merged with existing OLED components such as the substrate or encapsulation layers, rather than being added as a completely separate component. The scattering layer can be integrated into the bottom substrate or top encapsulation, combining multiple functions (structural support and light scattering) into a single element, thus reducing overall device complexity while maintaining high outcoupling efficiency.
Solution Approach 2:
The porous structure with air voids is implemented within a thin film layer that maintains mechanical flexibility and can be deposited using scalable processes. The porosity is controlled to optimize scattering while maintaining film integrity, allowing the complex optical function to be achieved with minimal additional structural complexity.
3Productivity
If phase inversion process is used to create porous film, then fabrication scalability is improved, but manufacturing precision of void distribution must be controlled
Solution Approach 1:
The phase inversion process parameters (such as immersion time, temperature, solvent composition, and crosslinking conditions) are optimized to control void size, density, and distribution. By adjusting these parameters, the manufacturing process achieves both scalability and precise control over the porous structure's optical properties, resolving the contradiction between productivity and manufacturing precision.
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 scattering layer increases outcoupling efficiency to approximately 65% in OLEDs, with improved color consistency across viewing angles and reduced fabrication costs, as the refractive index contrast between the host medium and air voids effectively redirects trapped light, enhancing optical power conversion.
Implementation Method 1
immersing the film and the substrate into an antisolvent bath for a first period of time so as to form a plurality of air voids within the film
Implementation Method 2
the host medium has a high refractive index as compared to a refractive index of the air voids... the refractive index contrast between the host medium and air voids effectively redirects trapped light
Data Source
AI summary
The present invention is directed towards a thin-film device. In one embodiment, the thin film device comprises a scattering layer comprising a substrate, the substrate comprising a plurality of voids, and a device stock formed atop the scattering layer, wherein the plurality of voids have a high refractive index as compared to a refractive index of the substrate. Another embodiment of the present invention is directed towards a process for fabricating a thin-film device, the process comprising dissolving a precursor in an organic solvent to form a solution, coating the solution onto a substrate to form a film, immersing the film and the substrate into an antisolvent bath for a first period of time so as to form a plurality of air voids within the film, removing the film and substrate from the anti-solvent bath to dry and cure for a second period of time to create a porous film adhered to the substrate, the porous film and the substrate forming a scattering layer.