Tandem OLED Driving Voltage Reduction via Energy Level Alignment
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Solution Overview
Problem
Organic light emitting diodes (OLEDs) with tandem structures face limitations due to high driving voltage, which hinders their efficiency and performance in display devices.
Innovation Solution
The implementation of an OLED structure that includes a first and second emitting part, separated by an n-type and p-type charge generation layer, where the first electron transporting layer has a higher lowest unoccupied molecular orbital (LUMO) energy level than the n-type charge generation layer, and the p-type charge generation layer has a higher LUMO energy level than the n-type charge generation layer, with a specific energy level difference to reduce the driving voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a tandem structure OLED is used to provide high emitting efficiency, then the emitting efficiency is improved, but the driving voltage becomes high
Solution Approach 1:
The patent changes the energy level parameters of the charge generation layers, specifically setting the LUMO energy level of the n-type charge generation layer lower than that of the first electron transporting layer by 0.3 to 1.0 eV. This parameter adjustment optimizes electron transport and reduces the driving voltage while maintaining high emitting efficiency in the tandem structure OLED
Solution Approach 2:
The patent introduces different types of charge generation layers (n-type and p-type) with distinct local properties at different positions between the emitting parts. The n-type charge generation layer is specifically designed with lower LUMO energy level to facilitate electron transport at the critical interface, creating localized quality differences that reduce overall device voltage
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 reduces the driving voltage of the OLED, enhancing its efficiency and performance by improving interfacial properties and energy level alignment, thereby addressing the high voltage limitations of tandem structure OLEDs.
Implementation Method 1
an n-type charge generation layer contacting the first electron transporting layer and positioned between the first electron transporting layer and the second emitting part; and a p-type charge generation layer contacting the n-type charge generation layer and positioned between the n-type charge generation layer and the second emitting part
Implementation Method 2
wherein the first electron transporting layer includes a first compound, and the n-type charge generation layer includes a second compound and an n-type dopant, and wherein a lowest unoccupied molecular orbital (LUMO) energy level of the first compound is higher than a LUMO energy level of the second compound, and a difference between the LUMO energy level of the first compound and the LUMO energy level of the second compound is 0.3 to 1.0 eV
Implementation Method 3
The OLED emits light by injecting electrons from a cathode as an electron injection electrode and holes from an anode as a hole injection electrode, both into an emitting material layer, combining the electrons with the holes, generating excitons, and transforming the excitons from an excited state to a ground state
Data Source
AI summary
An organic light emitting diode includes a first emitting part including a first emitting material layer (EML) and a first electron transporting layer (ETL), a second emitting part including a second EML and between the first emitting part and the second electrode, an n-type charge generation layer (CGL) contacting the first ETL and between the first ETL and the second emitting part, and a p-type CGL contacting the n-type CGL and between the n-type CGL and the second emitting part. The first ETL includes a first compound, and the n-type CGL includes a second compound and an n-type dopant. A lowest unoccupied molecular orbital (LUMO) energy level of the first compound can be higher than a LUMO energy level of the second compound.