Transparent Conducting Oxide Cathode for OLED Microcavity Elimination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Top-emission type organic light-emitting devices with metal cathodes exhibit microcavity structures, leading to luminance changes and color shifts with viewing angle, and require strict control of organic layer thickness, hindering mass production due to their high reflectivity and sensitivity to layer uniformity.
Innovation Solution
A top-emission type organic light-emitting device with a cathode formed as a transparent conducting oxide layer, such as indium oxide, using plasma-assisted thermal evaporation, eliminating microcavity effects and allowing for improved layer uniformity and reduced thermal damage to the organic functional layer, along with an electron injection enhancing layer to enhance electron injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal cathode (e.g., MgAg layer) is used to provide electron injection characteristics, then electron injection efficiency is improved, but microcavity structure is formed causing luminance change and color shift with viewing angle
Solution Approach 1:
The patent changes the material parameter of the cathode from metal to transparent conducting oxide (TCO), fundamentally altering the optical properties. TCO materials have different refractive indices and light interaction characteristics compared to metals, eliminating the microcavity effect while maintaining electrical functionality for electron injection.
Solution Approach 2:
The patent employs composite material structures including TCO layers combined with electron injection enhancing layers (such as LiF, Alq3, or BCP). This composite approach achieves both excellent electron injection efficiency and eliminates the harmful microcavity optical effects, resolving the contradiction between electrical performance and optical stability.
2Reliability
If a metal cathode is used, then electron injection is enhanced, but strict control of organic layer thickness (within 2% uniformity) is required
Solution Approach 1:
By changing the cathode material from metal to TCO, the patent alters the electrical and optical parameters of the device. TCO materials provide sufficient electron injection capability without creating the strong optical reflections that cause microcavity effects, thereby relaxing the manufacturing precision requirements for organic layer thickness control.
3Illumination intensity
If a transparent conducting oxide layer is used as cathode, then microcavity effects are eliminated and luminance stability is improved, but electron injection capability may be reduced
Solution Approach 1:
The patent introduces electron injection enhancing layers as intermediary materials between the TCO cathode and the organic light-emitting layer. These intermediary layers (such as LiF, Alq3, or BCP) have low work functions that facilitate electron injection from the TCO into the organic layer, compensating for the potentially lower electron injection capability of TCO materials compared to metals.
Solution Approach 2:
The patent creates a composite cathode structure combining TCO layers with electron injection enhancing layers. This composite material approach leverages the optical benefits of TCO (eliminating microcavity effects) while incorporating materials with favorable electrical properties for electron injection, thus achieving both luminance stability and efficient electron injection.
4Illumination intensity
If plasma-assisted thermal evaporation is used to form TCO cathode, then transmittance and conductivity are maintained without thermal damage to organic layers, but manufacturing process complexity increases
Solution Approach 1:
The patent utilizes plasma-assisted thermal evaporation, which involves phase transition processes. The plasma state provides ionized species that enhance deposition efficiency and film quality at lower substrate temperatures, preventing thermal damage to organic layers while achieving high transmittance and conductivity in the TCO cathode.
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
Prevents luminance and color shifts with viewing angle, facilitates mass production by eliminating microcavity effects, and maintains high transmittance and conductivity without damaging the organic layers, while enabling higher anode work functions for improved hole injection efficiency.
Implementation Method 1
The transparent conducting oxide layer may be formed using plasma-assisted thermal evaporation
Implementation Method 2
The holes and the electrons injected into the organic light-emitting layer are recombined to generate excitons, emitting light upon transition of the excitons from an excited state to a ground state
Data Source
AI summary
An organic light-emitting device including a transparent conducting oxide layer as a cathode and a method of manufacturing the organic light-emitting device. The organic light-emitting device includes an anode disposed on a substrate. An organic functional layer including at least an organic light-emitting layer is disposed on the anode. The transparent conducting oxide layer used as the cathode is disposed on the organic functional layer. The transparent conducting oxide layer cathode is formed by plasma-assisted thermal evaporation. A microcavity structure is not formed in the organic light-emitting device, thereby avoiding a luminance change and a color shift as a function of viewing angle.