David Savastano, Editor08.24.22
Inkjet printing displays has always been the a key goal for printed electronics. The advantages in terms of cost and manufacturing would be tremendous. However, it is easier said than done. On the OLED side, JOLED has had the most notable successes.
However, the thought of using inkjet printing for quantum dot-based displays makes a lot of sense. Quantum dots are solution-processed semiconductors, which can be jetted. There has been some noteworthy work done in the area of printing quantum dots, but commercialization isn’t there yet.
That is changing, though. Nanosys, the leading manufacturer of quantum dots, is reporting success in early stages of printing QD-based displays. Jeff Yurek, Nanosys’ VP of marketing, says that printing quantum dots is closer than people think.
“It will be sooner than you might imagine,” Yurek noted. “We’ve moved beyond early lab prototypes and are starting to see some super interesting work that looks a lot more like a real product. At the annual SID Display Week tradeshow back in May, there were a few prototype demonstrations of printed quantum dot displays being shown on the floor and in private suites. Nanosys’ partner BOE demonstrated a 55” 4K emissive quantum dot TV made using inkjet printing.”
There has always been the idea that printing displays would be a significant advantage for display manufacturers.
“Display makers have long been interested in printing,” said Yurek. “There have been efforts to try this at various times over the years, but printing has never taken off as a mass production process. There were several technical challenges– printing was hard to do both accurately and with the throughput needed for mass production at the massive scale the display industry operates.
“So why now? First, printing technology has improved tremendously, but I think, more importantly, quantum dots have provided the industry with a path to creating a nearly perfect display. That’s an exciting reason to take another look at printing,” he added.
Yurek observed that Quantum Dot Color Conversion (or QDCC) on top of blue OLED, sometimes called “QD-OLED,” is the first printed quantum dot application to be commercialized for displays.
“QD-OLED brings together two incredible technologies and takes the advantages of both – perfect contrast for OLED and lifelike color for quantum dots – to new heights,” Yurek reported. “It's a very different kind of viewing experience.
“When I saw a QD-OLED for the first time late last year, I knew that a new bar had been set. It’s unlike anything that has come before,” he added. “We’ve seen displays with perfect contrast, accurate color and lifelike brightness, wider viewing angles, etc. But we’ve never really seen all these attributes together in one display product.
“It’s exciting to see the first QD-OLED displays already on the market this year with products from Samsung, Sony, Dell Alienware, and MSI. This technology is a big step towards the future of low-cost, printed, emissive displays that we’re all driving towards.”
Inkjet printing is being used to print QD-OLED. Yurek pointed out that in a QD-OLED display, a layer of active, color-converting red and green quantum dots is printed on top of a blue-emitting OLED layer. The red and green quantum dots actively down-convert that blue light to create the precise RGB color at each pixel. This efficient color conversion, paired with the color purity of the light emitted by the quantum dots makes for a brighter, more colorful display that uses less power.
“The first step in producing a QD-OLED TV is to create a blue-emitting OLED ‘backlight’ on top of a backplane that controls the brightness of each pixel,” Yurek noted. “This OLED layer is produced using standard OLED evaporative processing. It covers the entire display with blue light emitters.
“This is where quantum dot printing comes in. An industrial-scale printer precisely prints quantum dot inks into tiny subpixels on another glass substrate that will then be bonded to the blue emitters.”
Several challenges need to be overcome to do this well.
“First, the printing process must be incredibly precise,” Yurek said. “A standard 4K TV of any size has nearly 8.3 million pixels. Each of those pixels is comprised of three subpixels, one each for red, green, and blue, for a total of 24.9 million light-emitting dots.
“The printer must also be fast. Today, QD-OLED is being produced at ‘Gen 8’ scale, which in display industry jargon, means huge 2.2 x 2.5 meter pieces of ‘motherglass’ that will eventually be cut into 65” and 55” TVs. Typical display fabs output tens of thousands of motherglass sheets per month. You start to do the math on this and you realize the printheads really need to be moving quickly to accomplish that kind of throughput, even if you have multiple lines running.”
Still, the advantages of printing displays using quantum dots make the process ideal for inkjet printing.
“One of the unique things about quantum dots is the way they are made,” Yurek said. “Quantum dots are solution-processed semiconductors. This makes them incredibly versatile. They can be formulated with solvents, monomers, polymer films, inks, photoresists, etc. so they are a natural fit for printing applications.
“Unlike traditional semiconductors, which are typically grown in the vapor phase, and on atomically flat wafers, quantum dots can be produced at a huge scale in chemical processing equipment,” he added. “This enables us to fabricate precise optical emitters at an extremely low cost compared to traditional semiconductor fabs. For comparison, if you were to make quantum dots on wafers, as traditional semiconductors are made, it would require more than 50 square meters of wafer area to make just 1 gram of quantum dots.”
Yurek noted that a few breakthroughs in quantum dot development were needed to make QD-OLED a reality as well.
“We worked closely with ink-making partners to compatibilize our quantum dots with printing inks,” he reported. “Quantum dots are incredibly small. Unlike all other phosphor materials, the smallest of which has a particle size in the few micron range, QDs are molecular-sized, meaning that they easily can flow through inkjet nozzles as part of the carrier ‘ink’ that is printed.
“Literally, the QDs are attached to the carrier ink, and they in turn provide incredible color conversion capability,” Yurek said. “We are able to make QDs compatible with the carrier ink so that the ink molecules attach to the QDs and the entire cluster comes out of the IJ nozzle beautifully so that the volume of dispense, and accuracy of the QDs in that volume from drop to drop, etc. is very precise.”
Yurek noted that printing quantum dots offers some compelling benefits compared to the lithography techniques used in making traditional displays.
“Basically, if you only put materials down where you need them, you can use less material, simplify the production process, and reduce your bill of materials,” he said. “If you look at the color filter manufacturing process for today’s LCD and WOLED TVs, both employ photolithography to pattern red, green, and blue filters on glass. Photolithography requires multiple steps, essentially covering the whole area of the display with each color, etching off the part you don’t need and starting again with the next color. Really, you are wasting two-thirds of your material in this process.”
As for the next steps in terms of using inkjet printing for displays, utilizing quantum dots will be key.
“QD-OLED has already been commercialized and the color conversion story is going to continue to be interesting as QDs are integrated into other types of displays in the near term,” Yurek said. “We are seeing a tremendous amount of activity and interest in patterning quantum dots on top of microLEDs as well as OLED. In microLEDs, printed QDs can help solve some of the manufacturing challenges around picking and placing millions of R, G and B pixels with no defects.
“Beyond color conversion is true, emissive quantum dot display,” Yurek concluded. “We call this technology NanoLED and it is sort of the holy grail of display technologies, with incredible performance from inorganic quantum dot emitter materials in terms of brightness, color and contrast. More importantly, it offers disruptively low cost since displays can be made entirely using solution processing. We can get rid of the costly evaporative steps and large vacuum chambers that are used in display making today. So that’s incredibly exciting and it’s not too far off. We are still a few years away from full commercialization but making rapid progress so stay tuned.”
However, the thought of using inkjet printing for quantum dot-based displays makes a lot of sense. Quantum dots are solution-processed semiconductors, which can be jetted. There has been some noteworthy work done in the area of printing quantum dots, but commercialization isn’t there yet.
That is changing, though. Nanosys, the leading manufacturer of quantum dots, is reporting success in early stages of printing QD-based displays. Jeff Yurek, Nanosys’ VP of marketing, says that printing quantum dots is closer than people think.
“It will be sooner than you might imagine,” Yurek noted. “We’ve moved beyond early lab prototypes and are starting to see some super interesting work that looks a lot more like a real product. At the annual SID Display Week tradeshow back in May, there were a few prototype demonstrations of printed quantum dot displays being shown on the floor and in private suites. Nanosys’ partner BOE demonstrated a 55” 4K emissive quantum dot TV made using inkjet printing.”
There has always been the idea that printing displays would be a significant advantage for display manufacturers.
“Display makers have long been interested in printing,” said Yurek. “There have been efforts to try this at various times over the years, but printing has never taken off as a mass production process. There were several technical challenges– printing was hard to do both accurately and with the throughput needed for mass production at the massive scale the display industry operates.
“So why now? First, printing technology has improved tremendously, but I think, more importantly, quantum dots have provided the industry with a path to creating a nearly perfect display. That’s an exciting reason to take another look at printing,” he added.
Yurek observed that Quantum Dot Color Conversion (or QDCC) on top of blue OLED, sometimes called “QD-OLED,” is the first printed quantum dot application to be commercialized for displays.
“QD-OLED brings together two incredible technologies and takes the advantages of both – perfect contrast for OLED and lifelike color for quantum dots – to new heights,” Yurek reported. “It's a very different kind of viewing experience.
“When I saw a QD-OLED for the first time late last year, I knew that a new bar had been set. It’s unlike anything that has come before,” he added. “We’ve seen displays with perfect contrast, accurate color and lifelike brightness, wider viewing angles, etc. But we’ve never really seen all these attributes together in one display product.
“It’s exciting to see the first QD-OLED displays already on the market this year with products from Samsung, Sony, Dell Alienware, and MSI. This technology is a big step towards the future of low-cost, printed, emissive displays that we’re all driving towards.”
Inkjet printing is being used to print QD-OLED. Yurek pointed out that in a QD-OLED display, a layer of active, color-converting red and green quantum dots is printed on top of a blue-emitting OLED layer. The red and green quantum dots actively down-convert that blue light to create the precise RGB color at each pixel. This efficient color conversion, paired with the color purity of the light emitted by the quantum dots makes for a brighter, more colorful display that uses less power.
“The first step in producing a QD-OLED TV is to create a blue-emitting OLED ‘backlight’ on top of a backplane that controls the brightness of each pixel,” Yurek noted. “This OLED layer is produced using standard OLED evaporative processing. It covers the entire display with blue light emitters.
“This is where quantum dot printing comes in. An industrial-scale printer precisely prints quantum dot inks into tiny subpixels on another glass substrate that will then be bonded to the blue emitters.”
Several challenges need to be overcome to do this well.
“First, the printing process must be incredibly precise,” Yurek said. “A standard 4K TV of any size has nearly 8.3 million pixels. Each of those pixels is comprised of three subpixels, one each for red, green, and blue, for a total of 24.9 million light-emitting dots.
“The printer must also be fast. Today, QD-OLED is being produced at ‘Gen 8’ scale, which in display industry jargon, means huge 2.2 x 2.5 meter pieces of ‘motherglass’ that will eventually be cut into 65” and 55” TVs. Typical display fabs output tens of thousands of motherglass sheets per month. You start to do the math on this and you realize the printheads really need to be moving quickly to accomplish that kind of throughput, even if you have multiple lines running.”
Still, the advantages of printing displays using quantum dots make the process ideal for inkjet printing.
“One of the unique things about quantum dots is the way they are made,” Yurek said. “Quantum dots are solution-processed semiconductors. This makes them incredibly versatile. They can be formulated with solvents, monomers, polymer films, inks, photoresists, etc. so they are a natural fit for printing applications.
“Unlike traditional semiconductors, which are typically grown in the vapor phase, and on atomically flat wafers, quantum dots can be produced at a huge scale in chemical processing equipment,” he added. “This enables us to fabricate precise optical emitters at an extremely low cost compared to traditional semiconductor fabs. For comparison, if you were to make quantum dots on wafers, as traditional semiconductors are made, it would require more than 50 square meters of wafer area to make just 1 gram of quantum dots.”
Yurek noted that a few breakthroughs in quantum dot development were needed to make QD-OLED a reality as well.
“We worked closely with ink-making partners to compatibilize our quantum dots with printing inks,” he reported. “Quantum dots are incredibly small. Unlike all other phosphor materials, the smallest of which has a particle size in the few micron range, QDs are molecular-sized, meaning that they easily can flow through inkjet nozzles as part of the carrier ‘ink’ that is printed.
“Literally, the QDs are attached to the carrier ink, and they in turn provide incredible color conversion capability,” Yurek said. “We are able to make QDs compatible with the carrier ink so that the ink molecules attach to the QDs and the entire cluster comes out of the IJ nozzle beautifully so that the volume of dispense, and accuracy of the QDs in that volume from drop to drop, etc. is very precise.”
Yurek noted that printing quantum dots offers some compelling benefits compared to the lithography techniques used in making traditional displays.
“Basically, if you only put materials down where you need them, you can use less material, simplify the production process, and reduce your bill of materials,” he said. “If you look at the color filter manufacturing process for today’s LCD and WOLED TVs, both employ photolithography to pattern red, green, and blue filters on glass. Photolithography requires multiple steps, essentially covering the whole area of the display with each color, etching off the part you don’t need and starting again with the next color. Really, you are wasting two-thirds of your material in this process.”
As for the next steps in terms of using inkjet printing for displays, utilizing quantum dots will be key.
“QD-OLED has already been commercialized and the color conversion story is going to continue to be interesting as QDs are integrated into other types of displays in the near term,” Yurek said. “We are seeing a tremendous amount of activity and interest in patterning quantum dots on top of microLEDs as well as OLED. In microLEDs, printed QDs can help solve some of the manufacturing challenges around picking and placing millions of R, G and B pixels with no defects.
“Beyond color conversion is true, emissive quantum dot display,” Yurek concluded. “We call this technology NanoLED and it is sort of the holy grail of display technologies, with incredible performance from inorganic quantum dot emitter materials in terms of brightness, color and contrast. More importantly, it offers disruptively low cost since displays can be made entirely using solution processing. We can get rid of the costly evaporative steps and large vacuum chambers that are used in display making today. So that’s incredibly exciting and it’s not too far off. We are still a few years away from full commercialization but making rapid progress so stay tuned.”