Quantum Dots are one of the most promising new technologies to emerge in the field of Electronics, especially for display technologies. They are a very promising alternative to traditional phosphor-based LCD and OLED displays and can be used in a variety of applications. In addition, these tiny, nanostructured particles are extremely thin, making them very lightweight, and can be shaped into different shapes and sizes. This is the key to their future potential as a viable option in the Display arena. As a result, Quantum Dots have become a hot topic in the industry, with numerous companies seeking to develop new products based on the technology.
Electroluminescent quantum dots
Electroluminescent quantum dots have many potential advantages over the traditional organic light-emitting diodes (OLEDs) in display applications. The future of electroluminescent QD-LEDs is bright.
Manufacturers are experimenting with other uses for these nanoscale particles, including energy-efficient LED lighting. EL QD-LEDs would allow manufacturers to achieve the same wide range of colors as OLEDs, but with more versatility. As they are less expensive and more readily available, they could become the next mainline display technology.
Nanosys has been partnering with leading emissive display companies to develop heavy metal-free QDs for EL QD-based displays. These new materials are cadmium-free and meet RoHS regulations, which require that a material be free of harmful chemicals such as cadmium. Other companies have begun developing materials containing indium, which is non-toxic and complies with RoHS.
Researchers have tested the performance of quantum dots in liquid solution. The results showed that the bandgap shrinked as temperature increased. This is a clear indication that temperature modulates the EL spectra. Since temperature changes the color of the emitted photons, the same phenomenon occurs in the QLEDs.
During the last year, Samsung has heavily promoted its own QLED technology. Using its proprietary color filter, the company has been able to produce some of the highest image quality on the market. While it is possible that these panels could also use cadmium QDs, Samsung’s research indicates that there are advantages to making these devices cadmium-free.
Nanosys and LG Display have worked on improving the device structure and core/shell/ligand system. The two companies have made major improvements to their EQE and QY values, which should result in better color gamut coverage.
Besides its ability to improve the performance of display technology, QD-OLED has the potential to solve decades of problems for large-screen TV makers. Using quantum dots to create the color filters for the TVs may help the manufacturers to make large panels without sacrificing the high image quality.
Down-converter approach
Quantum dots are tiny semiconductor particles that emit light at specific wavelengths. These particles have found applications in a wide range of modern day technologies.
A more advanced form of electroluminescent quantum dots is currently being developed. Electroluminescent quantum dots have the ability to produce displays with a high color purity and a wider color gamut. Furthermore, they have the potential to be cheaper than traditional LEDs and OLEDs. Therefore, these particles have the potential to replace conventional LEDs and OLEDs in TVs.
Besides being an ideal candidate for electroluminescent devices, colloidal quantum dots are able to produce displays with a high color purity. These devices are also effective sources of illumination.
Another route is to use a molecular seeding process to synthesize high-quality II-VI quantum dots. This method can produce kilogram batches of dots in just a few hours. But, the main limitation is that it does not offer precise control over the positioning of each dot.
Fabrication process technologies
Quantum dots (QDs) are a promising material for next-generation displays. They have unique optical and electronic properties that enable them to produce intense colors. For example, QDs emit blue, green, and red light, while some QDs also absorb ultraviolet light. This results in an impressive range of color gamuts. The EQE (emission quantum efficiency) of QD-based EL-LEDs ranges from 20.5% to 30.9% for blue, while that of phosphorescent OLEDs is between 30% and 60%.
Moreover, QDs have high photoluminescence quantum yields. These characteristics allow them to produce ultra-narrow linewidths, which are ideal for high-resolution display technology. However, the self-aggregation of QDs can cause a loss in efficiency. As a result, defect management plays a crucial role in display fabrication.
Another fabrication method involves spin casting. Spin casting produces better saturated green colors and thinner displays. But it also restricts lateral patterning of different sized QDs.
Finally, the most important factor in the display fabrication is defect management. Since the surface of the device has to be homogeneous, defect management is essential for preventing killer numbers from occurring during mass transfer.
While defect management is critical in the display manufacturing process, it is still a challenging issue. For example, the coffee-ring effect can lead to a non-uniform distribution of QDs on the LED’s surface. When there is a mismatch between the linewidth of the QDs and the substrate, the light from the LED will not be able to reach the pixel. If the mismatch is large, the display will be unstable.
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