Tungsten Oxide Hole Injection Layer for OLED Low-Voltage Operation
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Solution Overview
Problem
In organic EL display panels, the formation of hole injection layers on auxiliary wiring is hindered by high resistance and chemical instability, leading to increased manufacturing costs and reduced light-emitting efficiency due to the use of materials like copper phthalocyanine or PEDOT, which are difficult to pattern and prone to degradation.
Innovation Solution
A hole injection layer containing tungsten oxide is disposed continuously above the first electrode and auxiliary wiring, with an occupied energy level between 1.8 eV and 3.6 eV lower than the valence band, allowing for efficient carrier exchange and reducing the hole injection barrier, thus enabling low-voltage operation and stable performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hole injection layer is formed on auxiliary wiring using conventional materials (copper phthalocyanine or PEDOT), then carrier injection function is achieved, but resistance increases and chemical instability occurs
Solution Approach 1:
The patent changes the material parameter from conventional organic materials (copper phthalocyanine, PEDOT) to tungsten oxide, which has different electrical and chemical properties. This material substitution reduces resistance and improves chemical stability while maintaining the hole injection function.
Solution Approach 2:
The patent uses tungsten oxide as a composite material that combines the necessary electrical conductivity for hole injection with enhanced chemical stability and lower resistance, overcoming the limitations of single-material conventional injection layers.
2Productivity
If auxiliary wiring is provided to reduce resistance in wiring portions, then light emission efficiency improves, but manufacturing complexity increases due to patterning requirements
Solution Approach 1:
The hole injection layer made from tungsten oxide serves multiple functions: it provides hole injection to the functional layer, acts as an auxiliary wiring layer, and reduces resistance. This multi-functionality eliminates the need for separate patterning processes for auxiliary wiring, simplifying manufacturing.
Solution Approach 2:
The patent merges the hole injection layer with the auxiliary wiring structure by forming a continuous tungsten oxide layer that spans both the electrode and wiring regions, combining two previously separate functions into one integrated structure.
3Reliability
If conventional hole injection materials are used, then carrier injection is achieved, but light-emitting efficiency decreases due to material degradation
Solution Approach 1:
The patent changes the material composition from degradable organic materials to stable inorganic tungsten oxide, which maintains its electrical and chemical properties over time, thereby preserving light-emitting efficiency while continuing to provide effective carrier injection.
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 use of tungsten oxide in the hole injection layer reduces the hole injection barrier, enhances carrier exchange, and stabilizes the layer against degradation, resulting in improved light-emitting efficiency and reduced manufacturing complexity.
Implementation Method 1
the hole injection layer has, in an electronic state thereof, an occupied energy level in a range between 1.8 electron volts and 3.6 electron volts lower than a lowest energy level of a valence band of the hole injection layer in terms of a binding energy
Data Source
AI summary
The present invention provides an organic EL display panel and an organic EL display apparatus that can be driven at a low voltage and that exhibit excellent light-emitting efficiency. Sequentially fixated on a substrate are: a first electrode; auxiliary wiring; a hole injection layer; a functional layer; and a second electrode. The hole injection layer and the second electrode are both formed to be continuous above the first electrode and above the auxiliary wiring. The second electrode and the auxiliary wiring are electrically connected by the hole injection layer. The hole injection layer contains tungsten oxide and at least 2 nm thick so as to have, in an electronic state thereof, an occupied energy level in a range between 1.8 eV and 3.6 eV lower than a lowest energy level of a valence band in terms of a binding energy.