Yb Ag Cathode Structure for OLED Transmittance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional top-emitting OLED display devices face issues with high work function cathodes using transparent conductive materials and high resistance values when using semi-transmissive metal layers, which affect transmittance and emission efficiency.
Innovation Solution
A top-emitting OLED display device with a cathode formed by stacking ytterbium (Yb) and silver (Ag) layers, where Yb is deposited to a thickness of 20-30 Å and Ag to 70-90 Å, optimizing the thickness to achieve a sheet resistance of 45 ohm/square or lower and transmittance of 40% or more over the emission wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the upper electrode is formed of transparent conductive material such as ITO or IZO, then transmittance is improved, but work function is too high for cathode application
Solution Approach 1:
The patent applies composite materials by combining Yb and Ag in a layered structure. The Yb layer provides low work function (4.5 eV) suitable for electron injection as cathode, while the Ag layer enhances electrical conductivity. This composite structure resolves the contradiction by integrating materials with complementary properties that neither material alone can provide.
2Illumination intensity
If the upper electrode is formed of semi-transmissive metal layer such as MgAg, then transmittance is improved, but resistance value increases
Solution Approach 1:
The patent uses a composite structure of Yb and Ag layers where the Ag layer specifically addresses the resistance issue. Silver has excellent electrical conductivity, and by forming a separate Ag layer (70-90 Å thick) on top of the Yb layer, the patent achieves low resistance while maintaining the low work function property of Yb for electron injection.
Solution Approach 2:
The patent optimizes the thickness parameters of both Yb (20-30 Å) and Ag (70-90 Å) layers to achieve the desired balance between transmittance and resistance. By precisely controlling these thickness parameters, the patent achieves sheet resistance of 45 ohm/square or lower while maintaining transmittance of 40% or more.
3Reliability
If the cathode thickness is increased to reduce resistance, then resistance value is improved, but transmittance decreases
Solution Approach 1:
The patent segments the cathode into two distinct functional layers: a Yb layer (20-30 Å) responsible for electron injection due to its low work function, and an Ag layer (70-90 Å) responsible for electrical conductivity. This segmentation allows each layer to be optimized for its specific function without compromising the other, resolving the contradiction between resistance and transmittance.
Solution Approach 2:
The layered composite structure of Yb and Ag enables the system to achieve both low resistance and high transmittance simultaneously. The total thickness is controlled at 90-120 Å to maintain transmittance of 40% or more, while the Ag layer provides the necessary electrical conductivity with sheet resistance of 45 ohm/square or lower.
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 Yb/Ag cathode structure enhances transmittance and emission efficiency, minimizes microcavity effects, and ensures balanced color output when mixing different wavelengths, improving overall light emission characteristics.
Implementation Method 1
a second electrode being a cathode and including an ytterbium (Yb) layer formed on the organic layer and a silver (Ag) formed on the ytterbium layer
Data Source
AI summary
An organic light emitting diode (OLED) display device includes a substrate (100), a first electrode (110) disposed on the substrate, an organic layer (120) including an emission layer disposed on the first electrode, and a second electrode (130) including stacked layers of Yb and Ag on the organic layer. A method of fabricating the device is disclosed.