Organic Light-Emitting Device Optical Auxiliary Layer
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Solution Overview
Problem
Organic light-emitting devices face issues with contrast degradation and external light reflection due to metal electrodes and wires, which existing solutions like polarizing plates and compensation films address inadequately, especially concerning reliability and cost at varying temperatures.
Innovation Solution
Incorporating an optical auxiliary layer with a low refractive index and high absorption coefficient, made of materials like ytterbium, between the cathode and capping layer, to enhance light extraction efficiency and reduce external light reflection, along with a multi-layered capping structure for constructive interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal electrodes and metal wires are used in organic light-emitting devices, then electrical conductivity and device functionality are improved, but light reflection and contrast degradation occur
Solution Approach 1:
An optical auxiliary layer made of ytterbium is introduced between the metal cathode and the capping layer. This intermediary layer has a low refractive index (1.1-2.0) and high absorption coefficient (1-3) in the visible light region, effectively absorbing external light and preventing it from reflecting off the metal electrode. The layer thickness is optimized at 1-100 nm to achieve the desired optical properties while maintaining electrical functionality.
Solution Approach 2:
The patent changes the optical parameters of the interface between metal electrode and capping layer by introducing a layer with specifically controlled refractive index (1.1-2.0) and absorption coefficient (1-3). This parameter change transforms the reflective interface into an absorptive one, reducing light reflection and improving contrast ratio without affecting the electrical conductivity of the metal electrodes.
2Object-generated harmful factors
If polarizing plates and compensation films are applied to reduce external light reflection, then light reflection is reduced, but cost increases and reliability problems occur due to film property changes with temperature
Solution Approach 1:
The patent replaces expensive polarizing plates and compensation films with a thin layer of ytterbium (1-100 nm) that can be deposited directly onto the cathode. This approach eliminates the need for additional bulky optical films, reducing both cost and the risk of temperature-induced film property changes while effectively addressing light reflection issues.
3Illumination intensity
If an optical auxiliary layer with low refractive index and high absorption coefficient is introduced, then light extraction efficiency and contrast ratio are improved, but device structure complexity increases
Solution Approach 1:
Instead of modifying the entire device structure or adding multiple bulky layers throughout the device, the patent applies the optical auxiliary layer locally at the critical interface between the cathode and capping layer. This localized approach addresses the light extraction and reflection issues at the specific location where they occur most prominently, minimizing overall device complexity while achieving the desired optical performance.
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 improves light extraction efficiency and contrast ratio by absorbing external light, particularly in the visible spectrum, while maintaining high light emission efficiency without the reliability and cost issues of traditional solutions.
Implementation Method 1
the optical auxiliary layer may have a low refractive index and a high absorption coefficient as compared with those of the capping layer, in a visible light region
Implementation Method 2
a difference between the refractive index of the optical auxiliary layer and the refractive index of the capping layer may be in a range of about 0.5 to about 2.0 in a wavelength region between about 400 nm and about 550 nm
Data Source
AI summary
Provided is an organic light-emitting device including: a substrate; an anode on the substrate; an organic layer on the anode and including an emission layer; a cathode on the organic layer; an optical auxiliary layer on the cathode; and a capping layer on the optical auxiliary layer, wherein, in a visible light region, the optical auxiliary layer has a lower refractive index and a higher absorption coefficient as the capping layer.