OLED Luminescent Layer HOMO Level Adjustment for Drive Voltage Uniformity
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Solution Overview
Problem
In display units with organic electroluminescent devices of different colors, the varying thickness of luminescent layers leads to significant differences in drive voltages, resulting in inefficient power consumption as the power supply voltage needs to be adjusted to meet the highest required voltage, causing wasteful power consumption.
Innovation Solution
Incorporating an organic material with a similar highest occupied molecular orbital (HOMO) level as the hole-transport material into the luminescent layers, with increasing content as thickness increases, to reduce the resistance of the luminescent layers and level out drive voltages across devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the optical distance is adjusted only by the thickness of the luminescent layer, then the fabrication process is simplified and other layers can be commonly used, but the difference in thickness between luminescent layers of different colors increases, resulting in very large differences in drive voltages
Solution Approach 1:
The patent introduces an auxiliary layer with adjustable thickness and different refractive index to compensate for the optical path difference caused by varying luminescent layer thicknesses. By changing the thickness parameter of the auxiliary layer, the optical path length can be adjusted to achieve resonance conditions for different wavelengths without requiring large differences in luminescent layer thickness, thereby reducing drive voltage variations.
Solution Approach 2:
The patent employs a composite structure consisting of the luminescent layer and an auxiliary layer with different material properties (refractive index). This composite approach allows independent optimization of light emission properties and optical resonance conditions, enabling the system to achieve both color differentiation and voltage uniformity.
2Reliability
If the power supply voltage is set to meet the requirement of the device with the highest drive voltage, then all devices can be operated, but power is wastefully consumed due to the large difference between drive voltages
Solution Approach 1:
By adjusting the thickness of the auxiliary layer, the optical path length is optimized to reduce the difference in drive voltages between devices of different colors. This parameter adjustment enables all devices to operate at similar voltage levels, eliminating the need to set the power supply voltage to the highest requirement and thereby reducing power consumption.
3Illumination intensity
If luminescent layers of different thicknesses are used to adjust optical distance, then color purity and extraction efficiency are improved, but the resistance of luminescent layers varies significantly, requiring individual voltage adjustments
Solution Approach 1:
The auxiliary layer acts as an intermediary element that decouples the relationship between luminescent layer thickness and optical path length. This mediator allows the luminescent layer thickness to be optimized for light extraction efficiency while the auxiliary layer thickness is adjusted to achieve the desired optical resonance, eliminating the need for individual voltage adjustments.
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 approach allows for reduced drive voltages across organic electroluminescent devices with different thicknesses, minimizing the need for individual voltage adjustments, thereby decreasing power consumption and improving color reproducibility and luminance lifetime.
Implementation Method 1
the luminescent layer is thermally transferred onto the anode of the device substrate by irradiating the transfer substrate with laser light
Implementation Method 2
the luminescent layer is thermally transferred onto the anode of the device substrate
Implementation Method 3
the luminescent layer has a high resistance compared with the hole-transport layer which has a function of mainly transporting and injecting charges
Data Source
AI summary
A display unit and method of fabricating same are provided. The display unit includes a plurality of organic electroluminescent devices, each including an organic layer portion including at least a hole-transport layer and a luminescent layer which are stacked each other, and two electrodes sandwiching the organic layer portion. The luminescent layers of the individual organic electroluminescent devices have different thicknesses. The luminescent layer in each organic electroluminescent device contains an organic material having substantially the same HOMO level as that of a hole-transporting material constituting the hole-transport layer, the content of the organic material being set according to the thickness of the luminescent layer.