Insulator Layer Reduces Electron Injection Barrier in QLEDs
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Solution Overview
Problem
Conventional light-emitting elements face inefficiencies in electron injection due to deep-level defects and Fermi level pinning, leading to increased electron injection barriers, which hinder the efficient injection of electrons into the light-emitting layer, particularly in quantum-dot light-emitting diodes (QLEDs).
Innovation Solution
Incorporating an insulator layer with a relative permittivity of 2 or higher and 50 or lower, positioned between the electron-transport layer and the cathode, helps reduce charge movement and prevents Fermi level pinning, thereby reducing the electron injection barrier and enhancing electron injection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electron-transport layer is deposited by sputtering or application of nanoparticles, then the layer can transport electrons, but deep-level defects are formed on the surface and the Fermi level is pinned, creating a high electron injection barrier
Solution Approach 1:
The patent introduces an organic-metal-complex-containing layer as an intermediary between the electron-transport layer and the cathode. This intermediate layer undergoes redox reaction with the heat-reducing metal to form a reduction-induced layer that modifies the interface properties, preventing Fermi level pinning and reducing the electron injection barrier without compromising electron transport capability.
Solution Approach 2:
The patent changes the chemical and electronic parameters at the interface by introducing metal dopants into an organic matrix, creating an organic-metal-complex-containing layer. The redox reaction further modifies these parameters, transforming the interface from a high-barrier state to a low-barrier state that facilitates electron injection while maintaining transport efficiency.
2Reliability
If the Fermi level of the cathode is pinned to deep-level defects, then the work function becomes deep, but this creates a significantly higher electron injection barrier than expected from material properties
Solution Approach 1:
The organic-metal-complex-containing layer acts as a mediator that prevents direct interaction between the cathode and deep-level defects in the electron-transport layer. Through redox reaction with the heat-reducing metal, it forms a reduction-induced layer that serves as a buffer, allowing the cathode to maintain its original work function while enabling efficient electron injection.
Solution Approach 2:
The patent converts the potentially harmful effect of deep-level defects into a beneficial structure. By introducing the organic-metal-complex-containing layer that undergoes redox reaction, the interface is transformed so that the reduction-induced layer formed is electrically conductive and facilitates electron injection, turning what would be a defect-induced barrier into an injection-promoting interface.
3Reliability
If an organic-metal-complex-containing layer is used to reduce the electron injection barrier, then electron injection improves, but the reduction action causes defects on the surface of the layer
Solution Approach 1:
The patent introduces a second intermediate layer between the organic-metal-complex-containing layer and the cathode. This additional intermediate layer protects the surface of the organic-metal-complex-containing layer from damage during subsequent processing steps, preventing the formation of surface defects while preserving the electron injection enhancement achieved by the first intermediate layer.
Solution Approach 2:
The patent applies beforehand cushioning by introducing the protective intermediate layer that prevents surface damage to the organic-metal-complex-containing layer during subsequent cathode deposition or processing. This protective layer acts as a cushion that absorbs potential damage, preserving the surface integrity and electron injection properties of the underlying layer.
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 insulator layer effectively reduces the electron injection barrier, allowing for more efficient electron injection into the light-emitting layer, improving the overall performance of the light-emitting element by maintaining the original work function of the cathode and minimizing the impact of deep-level defects.
Implementation Method 1
The insulator layer has a relative permittivity of 2 or higher and 50 or lower
Data Source
AI summary
A light-emitting element includes: an anode, a light-emitting layer, a layer capable of transporting electrons, and a cathode, all of which are provided in a stated order; and an insulator layer provided in contact with, and at least partially between, the layer capable of transporting the electrons and the cathode, the insulator layer having a relative permittivity of 2 or higher and 50 or lower. The insulator layer includes a plurality of insulator layers shaped into islands and spaced apart from one another. The insulator layers are distributed non-uniformly in plan view.