Oxide Layer Dipoles for OLED Carrier Injection
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Solution Overview
Problem
Conventional light-emitting elements, such as OLEDs and QLEDs, face poor luminous efficiency due to difficulties in effectively injecting holes and electrons into the light-emitting layer, primarily because of high injection barriers and limited material options that affect band level adjustments.
Innovation Solution
A light-emitting element configuration that includes an anode, hole transport layer, light-emitting layer, electron transport layer, and cathode, with first and second oxide layers having different oxygen atom densities, which form electric dipoles to reduce injection barriers and enhance carrier injection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional materials are used for the light-emitting layer, hole transport layer, and electron transport layer, then long-term reliability is maintained, but the injection barriers (Eh1, Eh2, Ee1, Ee2) become high, making it difficult to efficiently inject carriers into the light-emitting layer
Solution Approach 1:
The patent introduces an organic layer between the inorganic light-emitting layer and the charge transport layers/ electrodes. This organic intermediary layer has adjustable HOMO and LUMO levels that can be optimized to reduce energy barriers for carrier injection, while the inorganic light-emitting layer maintains its long-term reliability. The organic layer acts as a buffer that facilitates carrier transfer without compromising the stability of the inorganic emitting material.
Solution Approach 2:
The patent changes the energy level parameters (HOMO and LUMO levels) of the interface between the light-emitting layer and charge transport layers by introducing the organic layer. By selecting organic materials with appropriate energy levels, the injection barriers Eh1, Eh2, Ee1, and Ee2 are reduced, enabling efficient carrier injection while maintaining the inorganic light-emitting layer's reliability.
2Reliability
If the material selection is limited to a small number of materials with long-term reliability, then device stability is ensured, but the choice of materials for optimizing band alignment and injection barriers is restricted
Solution Approach 1:
The patent segments the light-emitting device into distinct inorganic and organic components with different functions. The inorganic light-emitting layer provides long-term reliability and light emission, while the organic charge transport layers and interfacial organic layers provide material selection flexibility for optimizing energy level alignment and carrier injection. This functional segmentation allows each layer to be independently optimized.
Solution Approach 2:
The organic layers serve as intermediaries that decouple the material selection constraints. The inorganic light-emitting layer maintains reliability while the organic intermediary layers provide the versatility needed for band alignment optimization, allowing independent selection of materials based on their energy level characteristics without compromising the stability of the inorganic emitting layer.
3Loss of energy
If the band level of the light-emitting layer is adjusted by forming an organic ligand distribution with different surfaces, then the energy difference between valence band levels can be reduced, but the hole injection barrier Eh1 between the first electrode and hole transport layer cannot be effectively controlled
Solution Approach 1:
The patent introduces an organic layer as an intermediary between the inorganic light-emitting layer and the hole transport layer/first electrode. This organic intermediary provides independent control over the hole injection barrier Eh1 through its HOMO level, separate from the band level adjustments within the light-emitting layer itself. The organic layer's energy levels can be independently optimized to control carrier injection efficiency.
Solution Approach 2:
The patent changes the energy level parameters at the interface by introducing the organic layer. The HOMO and LUMO levels of the organic material can be independently selected to optimize both the hole injection barrier Eh1 and the energy difference within the light-emitting layer, providing versatile control over carrier injection and recombination processes.
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 significantly improves luminous efficiency by effectively controlling hole and electron injection into the light-emitting layer, leading to enhanced brightness and reduced drive voltage.
Implementation Method 1
first and second oxide layers having different oxygen atom densities, which form electric dipoles to reduce injection barriers and enhance carrier injection efficiency
Data Source
AI summary
A light-emitting element includes: a first electrode which is an anode, a hole transport layer, a light-emitting layer, an electron transport layer, and a second electrode which is a cathode in this order; and an oxide layer which is a first oxide layer and an oxide layer which is a second oxide layer disposed in this order from the first electrode side between the first electrode and the hole transport layer or between the electron transport layer and the second electrode, wherein a density of oxygen atoms in the second oxide layer is different from a density of oxygen atoms in the first oxide layer.