Electroluminescent Element Electric Field Annealing
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Solution Overview
Problem
In electroluminescent display panels, particularly of the top emission type, the formation of organic electroluminescent elements is hindered by damage to the underlying carrier transport layer during film forming methods like sputtering, and the introduction of a low work function metal layer between metal oxide and carrier transport layers leads to oxidation issues due to oxygen traces.
Innovation Solution
Applying electric field annealing processing with a current density of 50 to 375 A/m² and heating for 1 to 2 minutes to the electroluminescent element, including at least one organic compound layer and a counter electrode, improves luminance and light emitting efficiency by enhancing carrier injection properties through structural changes at the interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sputtering or electron beam method is used to form transparent conducting layer, then the layer can be formed successfully, but the underlying carrier transport layer is damaged
Solution Approach 1:
The patent applies inert atmosphere protection by introducing a low work function metal layer (such as aluminum, magnesium, or calcium) between the metal oxide transparent conducting layer and the organic carrier transport layer. This metal layer acts as a barrier that prevents oxygen from reaching and oxidizing the organic layer during sputtering or electron beam deposition processes, thereby protecting the carrier transport layer from damage while maintaining film forming quality.
Solution Approach 2:
The low work function metal layer serves as an intermediary layer that mediates between the metal oxide transparent conducting layer and the organic carrier transport layer. It provides a protective function by blocking oxygen diffusion while maintaining electrical conductivity, thus resolving the contradiction between successful film formation and protection of the underlying organic layer.
2Reliability
If low work function metal layer is added to improve carrier injection efficiency, then injection efficiency improves, but the metal layer is oxidized by trace oxygen
Solution Approach 1:
The patent positions the low work function metal layer as an intermediary between the metal oxide transparent conducting layer and the organic carrier transport layer. This strategic placement allows the metal layer to improve carrier injection efficiency into the organic layer while being protected from oxidation by the overlying metal oxide layer, which acts as an oxygen barrier.
Solution Approach 2:
The metal oxide transparent conducting layer creates an inert atmosphere environment for the underlying low work function metal layer by blocking oxygen diffusion. This protective configuration allows the metal layer to maintain its low work function properties and improve carrier injection without being oxidized by trace oxygen present in the processing environment.
3Area of stationary object
If top emission type structure is used to improve opening ratio, then opening ratio increases, but luminance and light emitting efficiency are reduced
Solution Approach 1:
The patent applies parameter changes by introducing a low work function metal layer that fundamentally alters the electrical properties at the interface between the transparent conducting layer and the organic carrier transport layer. This parameter change (work function) enables more efficient electron injection, which compensates for the reduced luminance in top emission type structures by improving overall light emitting efficiency through enhanced carrier balance.
Solution Approach 2:
The patent applies local quality improvement by adding the low work function metal layer specifically at the critical interface region where electron injection occurs. This localized modification targets the specific problem area (carrier injection efficiency) without changing the overall top emission type structure that provides the high opening ratio advantage, thus resolving the contradiction between opening ratio and luminance.
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 method enhances the luminance and light emitting efficiency of top emission type electroluminescent elements by improving electron injection properties and reducing the resistance at the injection barrier, leading to increased carrier transfer and efficient light emission.
Implementation Method 1
applying an electric field annealing processing that applies current within heating
Implementation Method 2
When a forward bias voltage is applied between the anode and cathode, an electron and a positive hole recombines in the organic compound layer, and the organic compound layer emits light
Data Source
AI summary
The present invention improves luminance and light emitting efficiency of electroluminescent elements. A manufacturing method of electroluminescent elements includes forming a positive electrode on a substrate, forming an organic compound layer on the positive electrode, forming an electron injecting layer on the organic compound layer, and forming a transparent conductive film on the electron injecting layer, thus forming electroluminescent element. After forming the transparent conductive film on the electron injecting layer, by applying a voltage between the positive electrode and the transparent conductive film while heating the electroluminescent element, light emission of the electroluminescent element such as luminance and light emitting efficiency is improved.