Light-Emitting Element Reducing Material Hole Injection
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Solution Overview
Problem
Current light-emitting elements face difficulties in efficiently injecting holes into the emission layer due to a high hole injection barrier, which is challenging to lower with existing materials and methods, particularly in quantum-dot light-emitting diodes where the ionization potential of the quantum-dot layer is around 5 eV or greater, requiring anode and hole-transporting materials with large ionization potentials that are still under development.
Innovation Solution
A light-emitting element configuration that includes a reducing-material-containing layer between the anode and the hole transport layer, which contains a reducing material that reduces the surface of the hole transport layer, forming deep defects and pinning the Fermi level, thereby increasing the effective work function of the anode and lowering the hole injection barrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional anode materials and hole-transporting materials are used, then the device structure is simple, but the hole injection barrier is high (5 eV or greater for quantum-dot layers), making efficient hole injection difficult
Solution Approach 1:
The hole transport layer is divided into multiple layers with different functions: a first hole transport layer in direct contact with the anode that provides high hole concentration and low injection barrier, and a second hole transport layer that transports holes to the emission layer. This segmentation allows each layer to be optimized for its specific function, resolving the contradiction between simple structure and efficient hole injection.
Solution Approach 2:
Different regions of the device are assigned different material properties: the first hole transport layer uses materials with high hole concentration (low activation energy p-type materials) to reduce the injection barrier at the anode interface, while the second hole transport layer uses materials optimized for hole transport to the emission layer. This local differentiation of material properties enables efficient hole injection without compromising overall device simplicity.
2Reliability
If anode materials with extremely large work function are used to lower the hole injection barrier, then hole injection efficiency improves, but such materials are difficult to obtain and manufacture
Solution Approach 1:
The first hole transport layer acts as an intermediary between the anode and the emission layer. It has high hole concentration that reduces the effective injection barrier, mediating the interface between conventional anode materials (with limited work function) and the quantum-dot emission layer (with high ionization potential). This intermediary layer enables efficient hole injection without requiring exotic anode materials with extremely large work function.
3Reliability
If hole-transporting materials with high hole density are used, then the hole injection barrier is lowered, but such materials are difficult to obtain due to compensation effects from p-type impurities
Solution Approach 1:
The invention changes the key parameter of hole concentration in the hole transport layer by selecting materials with low activation energy for p-type conduction. This parameter change enables achieving high hole density (10^19 cm^-3 or higher) without requiring difficult-to-obtain materials, as the low activation energy materials naturally provide high hole concentration through thermal excitation, overcoming the compensation effect from p-type impurities.
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 effectively lowers the hole injection barrier, improving the efficiency of hole injection into the emission layer by creating a deeper defect level that pins the Fermi level, allowing for a more effective work function and enhanced hole injection efficiency.
Implementation Method 1
The reducing-material-containing layer contains a reducing material that reduces the hole transport layer
Data Source
AI summary
A light-emitting element includes, in order of listing, an anode, an hole transport layer, an emission layer, and a cathode. The light-emitting element includes an reducing material disposed in at least a part between the anode and the hole transport layer, being in contact with the anode and the hole transport layer, and containing a reducing material that reduces a layer having the hole transport layer. The reducing material contains, in a structure of the reducing material, hydrogen either at a concentration ratio of 1 to 1 with resect to a base metal, or at a larger concentration ratio than the base metal.