OLED Second Electron Transport Layer LUMO Energy Level
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Solution Overview
Problem
Conventional organic light emitting diodes (OLEDs) face issues with luminous efficiency and contrast due to light emission during black color representation at low voltages, resulting in dim light emission and misrepresentation of black in dark environments.
Innovation Solution
Incorporating a second electron transport layer with a lower lowest unoccupied molecular orbital (LUMO) energy level than the first electron transport layer to suppress electron injection and transport at low voltages, maintaining a low current density and preventing light emission during black color representation, while allowing normal electron transport at higher voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electron transport layers are used with decreasing LUMO energy levels from opposite electrode to emission layer, then electron injection and transport are facilitated, but current density remains high at low voltage causing light emission during black color representation
Solution Approach 1:
The electron transport function is divided into two separate layers: a first electron transport layer adjacent to the emission layer, and a second electron transport layer adjacent to the opposite electrode. This segmentation allows each layer to have optimized LUMO energy levels for its specific function, resolving the contradiction between facilitating electron transport and suppressing low-voltage current leakage.
Solution Approach 2:
Different regions of the electron transport structure are assigned different LUMO energy level characteristics. The first electron transport layer has a higher LUMO energy level to suppress electron injection at low voltage near the emission layer, while the second electron transport layer has a lower LUMO energy level to facilitate electron transport from the opposite electrode. This local differentiation resolves the contradiction by optimizing each region's properties for its specific role.
2Reliability
If electron injection and transport are suppressed at low voltage to prevent light emission, then contrast and black color representation are improved, but electron transport efficiency may be reduced
Solution Approach 1:
The electron transport pathway is segmented into two layers with different energy level profiles. The first layer suppresses unwanted electron injection at low voltage to improve contrast, while the second layer maintains efficient electron transport from the electrode. This segmentation allows simultaneous optimization of both contrast ratio and electron transport efficiency without compromise.
Solution Approach 2:
The electron transport structure exhibits local quality differentiation where the first electron transport layer near the emission layer has higher LUMO energy levels for suppression functionality, while the second layer near the electrode has lower LUMO energy levels for efficient transport. This local optimization resolves the contradiction by allowing different regions to serve different functions.
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 prevents light emission during black color representation at low voltages, enhancing contrast and quality by maintaining a low current density, and ensures no difference in luminous efficiency compared to conventional OLEDs at higher voltages.
Implementation Method 1
In order to effectively perform injection or transport of electrons from the opposite electrode to the EML, one or a plurality of layers such as an electron transport layer (ETL) or electron injection layer (EIL) may be further interposed between the EML and the opposite electrode.
Implementation Method 2
layers interposed between the opposite electrode and the EML are generally disposed such that the absolute value of the lowest unoccupied molecular orbital (LUMO) energy level decreases in steps from the opposite electrode to the EML
Implementation Method 3
An organic light emitting diode, utilized as a self-emissive display
Data Source
AI summary
An organic light emitting diode (OLED) and a method of fabricating the same are provided. In the OLED, a second electron transport layer having an absolute value of a lowest unoccupied molecular orbital (LUMO) energy level smaller than that of a first electron transport layer is formed between a second electrode and the first electron transport layer, so that the second electron transport layer can suppress injection and transport of electrons under a low voltage condition to maintain a low current density. Accordingly, it is possible to prevent (or block) an element from emitting light when representing the color black. The OLED includes an emission layer on the first electrode, the first electron transport layer on the emission layer, the second electron transport layer on the first electron transport layer, and the second electrode on the second electron transport layer.