A team of researchers at the University of Minnesota has created the first 3D-printed flexible organic light-emitting diode (OLED) displays, measuring 1.5 inches by 1.5 inches with 64 pixels. The project is particularly interesting as it is a flexible screen that could be used to fold smartphone or TV screens, all at a more affordable cost. Two different additive manufacturing technologies and a custom printer were used to produce it.
Organic light-emitting diodes rely on organic materials to emit light, unlike LCD screens which use inorganic crystalline semiconductors. OLEDs are therefore an alternative to LCDs and have several interesting features: better energy efficiency by not requiring a backlight, high contrast ratio, mechanical flexibility, greater viewing angle and better resistance to breakage. However, 3D printing of such diodes has so far presented many challenges. OLED screen technology is based on the conversion of electricity into light using a layer of organic material. Creating this layer is difficult because it requires perfect uniformity, which is more difficult to achieve using additive manufacturing. Furthermore, polymer-metal bonds made by 3D printing are also more unstable.
Six 3D printed layers to form the OLED screen
The team used two 3D printing processes to overcome these challenges and create the six layers of the screen. Using an extrusion machine, they created the electrodes, insulation, interconnects, and encapsulation. The same 3D printer was then used to create the layers using a spray printing process. Specifically, the layers were successively printed from various materials, depending on the function of the layer in question. For example, the first layer was deposited on a flexible PET film and silver nanoparticles; the fourth layer is a silicone layer that covers the underlying conductive materials. Finally, the device was encapsulated with a polymer mold in an extrusion-printed silicone mold.
“In general, non-uniformity in active layers led to large variations in light emission in active regions within the same batch of devices, meaning a need for alternatives to extrusion printing for display fabrication. on a large scale. Therefore, we exploited a spray printing method to deposit MDMO-PPV to improve the uniformity of active layers. The spray nozzle was integrated into our printing system, so the ink was atomized into the orifice when a high relative velocity was created between the quasi-static ink and the pressurized sheath gas. The atomized droplets had diameters in the range of 30 to 50 μm and rapidly evaporated after impacting the substrate, resulting in the suppression of mass transport in the lateral direction. In the spray-printed active region, the droplets were evenly distributed over the target area and a substantial reduction in thickness variation was observed.” the team explained. The result was a flexible prototype 3.8 centimeters on a side, with 64 pixels capable of displaying light.
The researchers point out that the machine used was developed to measure and therefore incorporates different nozzles that are changed depending on the layer to be deposited. They are mounted on a robotic gantry system. All told, the machine would cost about the same as a Tesla Model S. Still, the printing method should evolve and become more widespread, according to Michael McAlpine, a senior professor in the Department of Mechanical Engineering at the University of Minnesota, who noted “OLED displays are typically produced in large, expensive, ultra-clean manufacturing facilities. This is something we actually make in the lab, and it’s not hard to imagine that it could translate to printing all kinds of screens ourselves at home or on the go in just a few years, on a small portable printer.”
While we wait to see what the future holds for display technologies, you can find the full study HERE. What do you think about the use of additive manufacturing to produce OLED screens? Let us know in a comment below or on our Linkedin, Facebook and Twitter pages! Don’t forget to sign up for our free weekly newsletter here, bringing the latest 3D printing news straight to your inbox! You can also find all our videos on our YouTube channel.
*Cover photo credits: McAlpine Group, University of Minnesota