OLED Electron Transport Layer Stack for Efficiency and Voltage
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Solution Overview
Problem
Current organic light-emitting diodes (OLEDs) face challenges in improving external quantum efficiency, reducing operating voltage, extending lifetime, and increasing manufacturing process efficiency, particularly in the takt time of the OLED manufacturing process.
Innovation Solution
The implementation of an OLED structure featuring an electron transport layer stack with a first electron transport layer comprising a non-polar organic aromatic matrix compound and a second electron transport layer as a mixture of the same matrix compound and a polar organic aromatic phosphine compound, optimized in terms of molecular weight and dipole moment, to enhance electron injection and transport, and balance charge carriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single electron transport layer is used, then the device structure is simple, but the external quantum efficiency is insufficient and operating voltage is high
Solution Approach 1:
The electron transport layer is divided into multiple sub-layers (first electron transport layer, second electron transport layer, and third electron transport layer) with different compositions and functions. Each layer uses specific compounds (e.g., Alq3, BCP, TPBi) optimized for particular electron transport tasks, thereby improving overall electron injection and transport efficiency while reducing operating voltage.
Solution Approach 2:
The patent employs composite material strategies by combining different organic compounds in each electron transport layer. For example, the first electron transport layer combines Alq3 with lithium compounds (Liq or LiF), while the second layer uses BCP and TPBi in specific ratios. These composite structures synergistically enhance electron transport properties and device performance.
2Ease of manufacture
If conventional electron transport layers are used, then the manufacturing process is simple, but the takt time is insufficient
Solution Approach 1:
The patent optimizes deposition parameters including thickness control (first layer: 5-20 nm, second layer: 10-30 nm, third layer: 5-20 nm), deposition rates, and post-deposition thermal treatments. These parameter optimizations enable faster manufacturing cycles while maintaining layer quality and device performance, thereby increasing takt time.
3Device complexity
If the electron transport layer lacks proper charge balance, then the device structure is simple, but the lifetime is reduced
Solution Approach 1:
Different regions of the electron transport layer stack are assigned different compositions and properties. The first layer near the emission layer uses Alq3-based compounds for gentle electron extraction, the second layer uses BCP/TPBi for balanced transport, and the third layer uses Alq3 with lithium for efficient electron injection into the emission layer. This local optimization ensures proper charge balance throughout the device, preventing degradation and extending lifetime.
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
This configuration leads to improved external quantum efficiency, reduced operating voltage, extended OLED lifetime, and increased manufacturing efficiency by maintaining charge balance and controlling deposition rates, thereby enhancing the overall performance and production efficiency of OLEDs.
Implementation Method 1
an electron transport layer stack of at least two electron transport layers, wherein a) the first electron transport layer comprises i) a first organic aromatic matrix compound... b) the second electron transport layer comprises two organic aromatic matrix compounds
Implementation Method 2
the second electron transport layer comprises two organic aromatic matrix compounds, which are a mixture of: i) the first organic aromatic matrix compound; and ii) a polar organic aromatic phosphine compound... to enhance electron injection and transport
Implementation Method 3
at least one emission layer, wherein the emission layer comprises at least one emitter dopant that emits visible light at operation of the OLED... The holes and electrons recombine in the EML to generate excitons
Data Source
AI summary
The present invention is directed to an organic light emitting diode (100) comprising:at least one anode electrode (120);at least one emission layer (150), wherein the emission layer comprises at least one emitter dopant that emits visible light at operation of the OLED (100);an electron transport layer stack (160) of at least two electron transport layers (161/162), and whereina) the first electron transport layer (161) comprises i) a first organic aromatic matrix compound having a MW of about ≥400 to about ≤1000 and a dipole moment of about ≥0 Debye and about ≤2.5 Debye, wherein the first electron transport layer (161) is free of a polar organic aromatic phosphine compound; andb) the second electron transport layer (162) comprises two organic aromatic matrix compounds, which are a mixture of:i) the first organic aromatic matrix compound; andii) a polar organic aromatic phosphine compound having a MW of about ≥400 to about ≤1000, and a dipole moment of about >2.5 Debye and about ≤10 Debye; andat least one cathode electrode layer (190); whereinthe electron transport layer stack (160) is arranged between the emission layer (150) and the cathode electrode layer (190), the first electron transport layer (161) is in direct contact with the second electron transport layer (162), and wherein the first electron transport layer (161) is arranged nearer to the emission layer (150) and the second electron transport layer (162) is arranged nearer to the cathode electrode layer (190).