The ability to print flexible displays is of significant interest to manufacturers. According to Research and Markets’ “Global Markets, Technologies and Applications for Flexible Displays,” by 2023, the market for flexible displays could top $12.6 billion. Combine printing with the fast-growing quantum dot technology, and the possibilities are virtually limitless.
 
In a major announcement, Nanosys and DIC recently reported a breakthrough using inkjet printing to produce quantum dot color conversion devices. This would be focused on LCD and emissive displays, such as microLEDs.
 
Minoru Hara, manager of DIC Corporation’s Marketing Division, noted that DIC has developed new inkjet inks for that make printing quantum dot (QD) displays possible. In terms of the partnership, Hara noted that Nanosys is developing cadmium-free quantum dot material adjusted to DIC’s inkjet ink, which is adjusted to inkjet printers. The inks can be jetted through a wide range of printheads using both UV and thermal curing.
 
“We developed brand new inkjet inks using several new materials, for example, adjusting ink to low viscosity required for fine patterning inkjet heads, keeping QD’s optical properties,” Hara observed. “We are proud it was possible to achieve because of the collaboration between Nanosys, the quantum dot materials leader, and DIC, the biggest manufacturer of inks.”
 
Russell Kempt, VP of sales and marketing at Nanosys, said that this breakthrough is the next step in the roadmap of quantum dot developments for the display industry.
 
“In the near term, high resolution, high efficiency, inkjet printable quantum dots bring enormous value to the LCD industry,” Kempt noted. “By replacing the color filters and moving the emitter to the front of the screen, LCD makers can create some exciting, differentiated new products with minimal investment. Quantum Dot Color Filter Replacement can roughly double the efficiency or brightness and deliver perfect color at any angle. Today’s printing developments will ultimately enable quantum dots to deliver on the promises made by oLED technology with truly low cost, rugged, flexible, emissive displays.”
 
The partners each bring key expertise to the project. DIC is the global leader in the field of printing inks, with a history of developing inkjet and electronic inks. Nanosys is a leader in the field of quantum dots, with 300 issued to pending patents and annual manufacturing capacity of more than 25 tons of quantum dot materials.
 
Power efficiency and improved color gamut are key benefits of quantum dots. Hara said that DIC believes there are two main advantages to color conversion layers printed by inkjet.
 
“First, cost reduction for QD materials through patterning RGB color conversion layer directly reduces the process through printing three colors at once,” said Hara. “Second, alkali-soluble resin is necessary for color resist ink for the printing process. Jet inks have a high degree of design freedom without requirement of alkali-soluble resin.”
 
Kempt pointed out that there will be performance and cost advantages to printing QD displays.
 
“Moving quantum dots to the front of the screen brings huge performance gains in color, brightness and viewing angle for display makers with very little investment,” Kempt said. “The reason for printing compared to other patterning methods like photo lithography is an inherent cost reduction. With inkjet printing, you simply put the material where you want it with little to no excess material waste.”
 
Hara noted that there are hurdles that have to be overcome, particularly color gamut and industry acceptance of inkjet printing.
 
“Regarding QD ink, there are some optimizations that both Nanosys and DIC are working on to optimize the color gamut performance,” Hara reported. “Another hurdle is one the industry must address, as this process will require panel makers to add new inkjet machines to their mass production lines, which could slow adoption.”
 
Kempt also noted that convincing companies that have spent hundreds of billions of dollars in current manufacturing equipment to move ahead with inkjet printing will be a hurdle.
 
“More than $200 billion has been spent to date installing manufacturing capacity for LCDs. It’s a lot to ask owners of these multi-billion dollar fabs to change their process in any significant way,” Kempt said. “Our goal was to make our quantum dots compatible with existing printing and patterning processes for making color filters. This required several technical breakthroughs for both the quantum dots and ink formulation.
 
“Color filters are not made under a vacuum today,” Kempt continued. “That meant our quantum dots needed to be what we call ‘air processable’ to make them compatible with the processing environment. Significant improvements in stability were required for quantum dots, a material that is typically protected from exposure to oxygen or moisture in other applications.
 
“We also needed to find a way to pack the quantum dots together very densely for this application,” he added. “The dots must absorb and convert all of the blue light coming from the backlight in one pass because any light leakage would reduce color purity. New surface chemistry needed to be developed for the dots so that we could pack them tightly together in an ultrathin layer with no loss in efficiency and no light leakage. Also, Nanosys has been leading the industry away from heavy metals so it was important to us to deliver this solution in a totally cadmium-free system.”
 
If this works out, Hara said that inkjet printing of displays using quantum dots could go public within the next two to three years.
 
Hara said that was the plenty of interest in the technology when the two companies showed it at the International Display Workshop and CES.
 
“Many people were interested in our joint development and came to our author interview session,” Hara said. “They were mainly interested in the workmanship of printed samples and how progress in improving green performance.”
 
“DIC presented at IDW and the response was very positive,” Kempt noted.  “We’re seeing a lot of interest in moving quantum dots to the front of the display due to huge performance gains with minimal capex relative to OLEDs. The demo we showed at CES was a hit as well. We demonstrated very fine patterning resolution of inkjet printed quantum dots equivalent to the pixel pitch on a 49” 4K TV.”
 
As for the future, Kempt said that Nanosys is working closely with DIC to further improve the color performance of the QD-ink and working with panel makers to make sure the QD-ink is compatible with their printers.
 
“We expect to see the first printed devices in the market within the next two years,” Kempt added. “Looking ahead, printed quantum dots can also help solve manufacturing yield issues for microLED displays, which today rely on a complex ‘pick and place’ process to create all three colors from millions of individual LEDs. With printed quantum dots we can simply the system, accelerating microLED technology’s path to market over the next couple of years.
 
“The future is even brighter,” Kempt said. “Printed emissive or electroluminescent quantum dots can really change how we think about our relationship with technology. We are thinking a lot about moving away from a device-centric world to a world of ‘Active Surfaces.’ These surfaces are interactive; they can display information or disappear into a home’s décor or even clothing. They need to be bright, power efficient, sensor-enabled and rugged. With true low-cost printing it may soon be possible to bring displays to markets and applications where today’s display technologies are either prohibitively expensive or too bulky.
 
“If we can get the cost of making a display down to $100 per square meter, which is basically the same cost as printing a high-resolution poster printing or a T-shirt, then displays could be everywhere,” Kempt concluded. “That’s our vision and we believe that the quantum dot material is the only material that has the opportunity to achieve this.”