Quantum Dots – Update
Since Quantum Dots are a current topic of conversations (see above), we thought it helpful to update readers on the current state of the QD space relative to display. Quantum Dots themselves are nano-structures that are typically composed of a core material and a shell. What makes quantum dots interesting is they are the shape-shifters of the display space, well maybe not shape-shifter but color shifter. By stimulating a quantum dot, either optically or electrically, the quantum dot will emit light. In the case of QDs, the actual size of the QD will determine the color that it emits, with the largest QDs emitting red and the smallest blue, so by controlling the size of the dots during production, they can be tailored to emit specific colors.
A secondary characteristic of quantum dots is that they produce ‘precise’ colors, essentially colors that produce light at narrow wavelengths, under 50nm wide in most cases, as opposed to OLED materials that produce similar peaks but broader bases, giving display designers the ability to tailor the color balance to very tight specifications.
A secondary characteristic of quantum dots is that they produce ‘precise’ colors, essentially colors that produce light at narrow wavelengths, under 50nm wide in most cases, as opposed to OLED materials that produce similar peaks but broader bases, giving display designers the ability to tailor the color balance to very tight specifications.
Wavelength FWHM Comparison - QD/OLED - Source: Recent advances in quantum dot-based light-emitting devices: Challenges and possible solutions,
A 3rd characteristic of quantum dots is that when they are used to ‘color convert’ there is minimal loss of energy compared to color filters, which reduce light output by as much as 66%. This means that when a quantum dot is ‘pumped’ (stimulated to emit light) by a light source, much of that light is converted rather than blocked, resulting in a brighter and more color saturated display. This is theory behind Samsung Display’s QD/OLED display panels mentioned above. In these large panels, a layer or multiple layers of OLED material, typically blue or blue and green, are spread across a substrate while red and green quantum dots are patterned above the OLED material. In the case where the OLED material emits blue light, every third space in the quantum dot patterning is left open to allow blue light from the OLED emitter to pass through, while the red and green quantum dots convert the blue light to red and green.
There will be many variants on the structure of such panels but the theory is that the blue OLED light ‘pumps’ the quantum dots to emit their respective colors, creating a large panel RGB display without the deposition limitations that keep RGB OLED from being used for OLED TVs. In the case of SDC’s QD/OLED display, the quantum dots are patterned using an ink jet printer, with the dots being dissolved in a solvent along with wetting agents. This allows the entire substrate to be patterned without the metal masks used in small panel RGB OLED production and is extremely efficient in the use of materials., while able to create dots at intervals down to 2um, meaning there are few patterning limitations as to display resolution.
All in, the result should be a brighter overall panel that retains the high contrast of a self-emissive display and the color purity that quantum dots provide, however while this sounds relatively easy, the engineering behind such a device is complex. The TFT that drive the OLED material to emit light is different than what is typically used for LTPS or LTPO backplanes used for LCD and OLED displays, so the design of the backplane for QD/OLED was a daunting task, and while ink jet printing has been used to encapsulate OLED materials, patterning at such tight tolerances required a substantial improvement in IJP tools and considerable research in QD ink composition, which will continue as the materials and process move into mass production.
That said, after the initial release of Sony’s QD/OLED TV and the potential Samsung set, the question will be whether the public will see enough of a difference in the display to rationalize what will likely be a higher cost relative to WOLED. Initial reports from some trusted sources who have seen physical demos are quite favorable, however all the positive reviews in the world are secondary to what the buyer sees when walking into a store, and the answer to those questions will likely not be answered until later this year. There will likely be strong pre-order sentiment from sagacious technocrats, but rank and file buyers are needed to sell enough units to justify the production expansion necessary to establish the technology as a potential display modality and to support the continuation of the R&D necessary to reduce costs and make material and manufacturing improvements. More on QDs tomorrow.
There will be many variants on the structure of such panels but the theory is that the blue OLED light ‘pumps’ the quantum dots to emit their respective colors, creating a large panel RGB display without the deposition limitations that keep RGB OLED from being used for OLED TVs. In the case of SDC’s QD/OLED display, the quantum dots are patterned using an ink jet printer, with the dots being dissolved in a solvent along with wetting agents. This allows the entire substrate to be patterned without the metal masks used in small panel RGB OLED production and is extremely efficient in the use of materials., while able to create dots at intervals down to 2um, meaning there are few patterning limitations as to display resolution.
All in, the result should be a brighter overall panel that retains the high contrast of a self-emissive display and the color purity that quantum dots provide, however while this sounds relatively easy, the engineering behind such a device is complex. The TFT that drive the OLED material to emit light is different than what is typically used for LTPS or LTPO backplanes used for LCD and OLED displays, so the design of the backplane for QD/OLED was a daunting task, and while ink jet printing has been used to encapsulate OLED materials, patterning at such tight tolerances required a substantial improvement in IJP tools and considerable research in QD ink composition, which will continue as the materials and process move into mass production.
That said, after the initial release of Sony’s QD/OLED TV and the potential Samsung set, the question will be whether the public will see enough of a difference in the display to rationalize what will likely be a higher cost relative to WOLED. Initial reports from some trusted sources who have seen physical demos are quite favorable, however all the positive reviews in the world are secondary to what the buyer sees when walking into a store, and the answer to those questions will likely not be answered until later this year. There will likely be strong pre-order sentiment from sagacious technocrats, but rank and file buyers are needed to sell enough units to justify the production expansion necessary to establish the technology as a potential display modality and to support the continuation of the R&D necessary to reduce costs and make material and manufacturing improvements. More on QDs tomorrow.
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