OLED Light Extraction via Curved Substrate and Charge Injection Layer
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Solution Overview
Problem
Electroluminescent devices suffer from low light output efficiency due to total internal reflection, with existing techniques failing to redirect all trapped light rays to angles less than the critical angle for escape, and the use of silver or silver-based alloys as reflective electrodes leads to premature shorting and spreading losses.
Innovation Solution
Incorporating a charge injection layer adjacent to the silver or silver-based alloy reflective electrode and a thin, transparent short-reduction layer with appropriate electrical resistivity, along with a light extraction enhancement structure and a device size significantly larger than the substrate thickness to enhance light extraction efficiency and prevent shorting failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If light extraction enhancement structures are used to increase light output, then light extraction efficiency is improved, but device complexity increases
Solution Approach 1:
The patent applies curvature to the substrate surface by forming a convex lens array or microlens structure. These curved optical elements refract and redirect trapped light rays at the substrate-air interface, converting substrate-mode light and organic-mode light into air-mode light that can escape the device. This optical curvature solution effectively increases light extraction efficiency without requiring complex internal modifications to the OLED structure.
Solution Approach 2:
The patent introduces a new dimensional approach by adding surface relief structures (convex lenses) on the substrate exterior rather than modifying internal layers. This external optical dimension allows light redirection without interfering with the internal electrode and organic layer configuration, thereby improving light extraction while maintaining structural simplicity.
2Productivity
If silver or silver-based alloys are used as reflective electrodes to improve light reflection, then light output is improved, but premature shorting occurs
Solution Approach 1:
The patent introduces an intermediary charge injection layer between the silver reflective electrode and the organic light-emitting layers. This intermediary layer serves dual functions: it prevents direct contact between the silver electrode and organic materials that would cause shorting, and it facilitates charge injection into the organic layers. This mediator resolves the reliability issue while preserving the optical benefits of silver.
Solution Approach 2:
The patent employs a thin charge injection layer that can be easily deposited and removed if necessary. This sacrificial-like layer provides temporary protection during device operation, preventing shorting without compromising the long-term performance of the silver electrode. The layer is designed to be thin and simple, allowing for easy manufacturing and replacement if needed.
3Productivity
If device size is increased to reduce spreading losses, then light output efficiency is improved, but manufacturing cost increases
Solution Approach 1:
The convex lens array on the substrate surface acts as an optical concentrator that redirects spreading light rays back toward the viewer. This curvature-based optical management reduces spreading losses without requiring a larger device area, thereby maintaining manufacturing efficiency while improving light output 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
The solution effectively increases light extraction efficiency, reduces premature shorting, and minimizes spreading losses, resulting in improved operating lifetime and light output for electroluminescent devices.
Implementation Method 1
Light is generated in the electroluminescent device when electrons and holes that are injected from the two electrodes flowing through the light-emitting element and generating light by either recombination or impact ionization
Implementation Method 2
Incorporating a charge injection layer adjacent to the silver or silver-based alloy reflective electrode and a thin, transparent short-reduction layer with appropriate electrical resistivity, along with a light extraction enhancement structure and a device size significantly larger than the substrate thickness to enhance light extraction efficiency
Implementation Method 3
a reflective second electrode layer... It has been estimated that more than 50% of light generated by the light-emitting layer ends up as the organic mode of light, more than 30% ends up as the substrate mode of light, and less than 20% of light from the light-emitting layer is outputted into the air and becomes useful light
Data Source
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AI summary
An OLED device including a transparent substrate (10) having a first surface and a second surface, a transparent electrode layer (12) disposed over the first surface of the substrate, a short reduction layer (50) disposed over the transparent electrode layer, an organic light-emitting element (30) disposed over the short reduction layer and including at least one light-emitting layer (35) and a charge injection layer (37) disposed over the light emitting layer, a reflective electrode layer (22) disposed over the charge injection layer and a light extraction enhancement structure (40) disposed over the first or second surface of the substrate; wherein the short reduction layer is a transparent film having a through-thickness resistivity of 10-9 to 102 ohm-cm2; wherein the reflective electrode layer includes Ag or Ag alloy containing more than 80 % of Ag; and the total device size is larger than 10 times the substrate thickness.