Stacked Organic Light-Emitting Diode with NP Conjunction
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Solution Overview
Problem
Existing organic light emitting devices face challenges in stabilizing the interface between electrodes and organic layers, leading to increased driving voltage and reduced performance due to energy barriers for hole injection, which limits material selection and affects charge transport efficiency.
Innovation Solution
A stacked organic light emitting diode structure with NP conjunction between n-type and p-type organic layers, where an n-type doped organic layer is interposed between light emitting units, reducing the energy barrier for hole injection and allowing for the use of various materials for electrodes, thereby simplifying the manufacturing process and enhancing brightness and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional electrode interface structure is used, then the device structure is simple, but the energy barrier for hole injection is high and the interface is unstable
Solution Approach 1:
The device is divided into multiple functional segments: electrode, electron injection layer, electron transport layer, light emitting layer, and hole transport layer. Each layer has a specific function and is optimized independently, allowing the interface stability issue to be addressed at the electron injection layer without affecting the overall device structure
Solution Approach 2:
An electron injection layer is introduced as an intermediary between the electrode and the electron transport layer. This intermediate layer serves as a buffer that stabilizes the interface and facilitates charge injection, resolving the instability problem without requiring complex structural modifications
2Power
If the energy level difference between electron/hole injection layer and adjacent organic layer is not controlled, then the device structure is simple, but the driving voltage is high
Solution Approach 1:
The energy levels of the organic layers are systematically adjusted to achieve optimal charge injection. The electron transport layer is designed with LUMO level 2.0-3.5 eV and HOMO level 5.5-7.0 eV, while the hole transport layer is designed with LUMO level 2.5-4.0 eV and HOMO level 5.0-6.5 eV. These parameter optimizations reduce the driving voltage without complicating the manufacturing process
Solution Approach 2:
Different regions of the device are assigned different energy level characteristics tailored to their specific functions. The electron transport layer has optimized LUMO levels for electron injection, while the hole transport layer has optimized HOMO levels for hole transport. This localized optimization reduces overall driving voltage while maintaining manufacturing simplicity
3Reliability
If the charge carrier concentration in organic layer is low, then the material selection is wide, but the contact resistance is high and charge transport is inefficient
Solution Approach 1:
The charge carrier concentration in the organic layers is optimized to achieve efficient charge transport. By adjusting doping concentrations and selecting materials with appropriate mobility characteristics, the contact resistance is reduced while maintaining a wide range of material selection for manufacturing
Solution Approach 2:
The successful interface structure and energy level configuration are replicated between the electron and hole transport layers. This copying of the optimized architecture ensures consistent charge transport efficiency across different parts of the device without requiring entirely new material selections
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 NP conjunction structure lowers the energy barrier for hole injection, improves charge transport, and allows for high brightness and low driving voltage operation, enabling efficient charge balancing and increased light emitting efficiency across multiple light emitting units without the need for additional conductive layers.
Implementation Method 1
A stacked organic light emitting diode structure with NP conjunction between n-type and p-type organic layers, where an n-type doped organic layer is interposed between light emitting units, reducing the energy barrier for hole injection
Implementation Method 2
The organic light emitting device converts a current into visible rays by injecting electrons and holes from two electrodes into the organic layer
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
The present invention provides a stacked organic light emitting diode that comprises a first electrode; a second electrode; and at least two light emitting units that are located between the first electrode and the second electrode. The light emitting unit satisfies the following energy relation equation, and includes an n-type organic layer and a p-type organic layer that form NP conjunction, and also includes an n-type doped organic layer that is located between the light emitting units: EpH-EnL≤1eV wherein EnL is a LUMO (lowest unoccupied molecular orbital) energy level of the n-type organic layer and EpH is a HOMO (highest occupied molecular orbital) energy level of the p-type organic layer.