OLED Composite Electron Injection Layer for Inverted Display Efficiency
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Solution Overview
Problem
Organic light-emitting diodes (OLEDs) face challenges with lower luminous efficiency and higher driving voltage due to inferior electron injection characteristics, particularly in inverted OLEDs when coupled to n-type transistors, leading to image sticking and suboptimal performance.
Innovation Solution
Incorporating a composite electron injection layer with a low work function metal layer and a metal complex layer having carrier injection capabilities, directly formed on the cathode, improves electron injection characteristics, reducing driving voltage and enhancing luminous efficiency and lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an inverted organic light-emitting diode is coupled to a drain electrode of an n-type transistor, then image sticking phenomenon is prevented, but luminous efficiency decreases and driving voltage increases
Solution Approach 1:
The patent applies composite materials by creating a dual-layer electron injection layer comprising a first electron injection layer and a second electron injection layer with different material compositions and properties. The first layer (e.g., LiF, Alq3) provides good electron injection, while the second layer (e.g., BPhen, Bpy-OH) enhances electron transport and reduces trapping. This composite structure resolves the contradiction by maintaining the inverted OLED connection to n-type transistors (preventing image sticking) while improving overall electron injection efficiency to restore luminous efficiency.
Solution Approach 2:
The patent applies local quality by optimizing the electron injection layer structure specifically at the cathode interface where electron injection occurs. By introducing a specialized two-layer electron injection structure only at this critical location rather than throughout the entire device, the patent locally enhances electron injection performance to reduce driving voltage and improve luminous efficiency, while maintaining the beneficial inverted connection topology for preventing image sticking.
2Reliability
If an inverted organic light-emitting diode is coupled to a drain electrode of an n-type transistor, then image sticking phenomenon is prevented, but driving voltage increases
Solution Approach 1:
The patent applies composite materials by creating a dual-layer electron injection layer comprising a first electron injection layer and a second electron injection layer with different material compositions and properties. The first layer (e.g., LiF, Alq3) provides good electron injection, while the second layer (e.g., BPhen, Bpy-OH) enhances electron transport and reduces trapping. This composite structure resolves the contradiction by maintaining the inverted OLED connection to n-type transistors (preventing image sticking) while improving overall electron injection efficiency to restore luminous efficiency.
Solution Approach 2:
The patent applies parameter changes by modifying the electronic properties of the electron injection layer through material selection and layer structure optimization. By changing the work function, electron mobility, and energy level alignment parameters of the injection layer materials, the patent reduces the energy barrier for electron injection, thereby lowering driving voltage while maintaining the inverted connection configuration that prevents image sticking.
3Loss of energy
If a standard organic light-emitting diode is coupled to a source electrode of an n-type transistor, then higher luminous efficiency is achieved, but image sticking phenomenon occurs
Solution Approach 1:
The patent applies inversion by reversing the conventional connection topology: instead of connecting the OLED anode to the source electrode of an n-type transistor (standard configuration), the patent connects the OLED cathode to the drain electrode of the n-type transistor (inverted configuration). This inversion prevents image sticking by eliminating the charge accumulation at the transistor-OLED interface. The patent further resolves the resulting efficiency loss by introducing an optimized dual-layer electron injection structure at the cathode to compensate for the inverted connection's impact on electron injection.
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 composite electron injection layer significantly reduces driving voltage and increases luminous efficiency and lifetime of OLEDs, making them more suitable for use in display devices while preventing image sticking.
Implementation Method 1
the cathode injects electrons into the light-emitting layer
Implementation Method 2
a metal complex layer having carrier injection capabilities
Implementation Method 3
When the electrons recombine with the holes in the light-emitting layer, excitons are formed. Recombination of the electron and hole results in light emission.
Data Source
AI summary
An organic light-emitting diode and a display device employing the same are provided. The organic light-emitting diode includes a substrate; a cathode disposed on the substrate; an electron injection layer disposed on the cathode, wherein the electron injection layer includes a low work function metal layer and a metal complex layer having carrier injection capability; a light-emitting layer disposed on the electron injection layer; and an anode disposed on the light-emitting layer.