We all know that OLED has found promising applications in flat-panel displays, replacing the cathode ray tubes (CRTs) or LED displays. Solid-state OLEDs make it easier to fabricate flexible displays. OLED displays feature great image quality – bright colors, fast motion and most importantly – very high contrast. They are lightweight, power-efficient, thin and flexible, and offer a wide viewing angle and high contrast ratio.
OLED
Organic light-emitting diodes (devices) or OLEDs are monolithic, solid-state devices. It consists of a series of organic thin films sandwiched between two thin-film conductive electrodes. When electricity is applied to an OLED, under the influence of an electrical field, charge carriers (holes and electrons) migrate from the electrodes into the organic thin films until they recombine in the emissive zone forming excitons. Once formed, these excitons, or excited states, relax to a lower energy level by giving off light (electroluminescence) and/or unwanted heat.
Manufacturing of OLED
Flexible OLED is manufactured using the vacuum deposition method. Anodes are applied to a substrate material of plastic or glass. Organic, conductive molecules dispersed throughout a solvent are then applied to the anode, commonly through inkjet processing.
Inkjet processing is a relatively cheap and repeatable manufacturing method that is used for a range of printing methods, from photographs to printed circuitry. In the case of OLEDs, inkjets spray the substrate material with a specialty dispersion, coating it with a uniform layer of conductive molecules. A second layer is then added to the matrix through similar processes, this one is comprised of emissive molecules – and further layers can be applied if necessary.
So, is it possible to fully 3D print a flexible OLED display at home? Check it out below.
Groundbreaking Study
Researchers at the University of Minnesota Twin Cities used a customized printer to fully 3D print a flexible organic light-emitting diode (OLED) display. The discovery could result in low-cost OLED displays in the future that could be widely produced using 3D printers by anyone at home, instead of the technicians manufacturing with the expensive microfabrication facilities.
“We wanted to see if we could basically condense all of that down and print an OLED display on our table-top 3D printer, which was custom built and costs about the same as a Tesla Model S”, said Michael McAlpine, a University of Minnesota Kuhrmeyer Family Chair Professor in the Department of Mechanical Engineering and the senior author of the study.
The group had previously tried 3D printing OLED displays, but they struggled with the uniformity of the light-emitting layers. Other groups partially printed displays but also relied on spin-coating or thermal evaporation to deposit certain components and create functional devices.
The University of Minnesota research team combined two different modes of printing to print the six device layers that resulted in a fully 3D-printed, flexible organic light-emitting diode display. The electrodes, interconnects, insulation, and encapsulation were all extrusion printed, while the active layers were spray printed using the same 3D printer at room temperature. The display prototype was about 1.5 inches on each side and had 64 pixels. Every pixel worked and displayed light.
Researchers’ Viewpoint
“I thought I would get something, but maybe not a fully working display,” said Ruitao Su, the first author of the study and a 2020 University of Minnesota mechanical engineering Ph.D. graduate. “But then it turns out all the pixels were working, and I can display the text I designed. My first reaction was ‘It is real!’ I was not able to sleep, the whole night.”
“The device exhibited a relatively stable emission over the 2,000 bending cycles, suggesting that fully 3D printed OLEDs can potentially be used for important applications in soft electronics and wearable devices,” Su said.
The researchers said the next steps are to 3D print OLED displays that are higher resolution with improved brightness.
“The nice part about our research is that the manufacturing is all built in, so we’re not talking 20 years out with some ‘pie in the sky’ vision,” McAlpine said. “This is something that we actually manufactured in the lab, and it is not hard to imagine that you could translate this to printing all kinds of displays ourselves at home or on the go within just a few years, on a small portable printer.”
In addition to McAlpine and Su, the research team included University of Minnesota mechanical engineering researchers Xia Ouyang, a postdoctoral researcher; Sung Hyun Park, who is now a senior researcher at Korea Institute of Industrial Technology; and Song Ih Ahn, who is now an assistant professor of mechanical engineering at Pusan National University in Korea.
Possibilities
It would seem feasible for this technology to be parallelized to the extreme. Imagine instead of a single printhead depositing material we had a line of deposition heads that operate in parallel. As the printhead sweeps across a deposition surface, tens or perhaps even hundreds of pixels could be built simultaneously. This approach could certainly speed up throughput on a future hypothetical OLED display 3D printer.
Another possibility for this technology is to incorporate it into existing 3D print technology. Imagine a device that can not only print a mechanical structure, but also electronics and OLED displays or lighting. That’s getting dangerously close to being able to 3D print completely functional electronic objects. On the other hand, all it would need is a blueprint of the objects that you want to print and boom! it would be there; not to mention the copyright issues that would come with it.
As of this writing, a Model S would cost between US$88K all the way up to US$124K, so in other words, a bit more expensive than typical desktop 3D printers. However, far less than the cost of the standard fabrication plant for OLED panels.
Funds
The research was funded primarily by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health (Award No. 1DP2EB020537) with additional support from The Boeing Company and the Minnesota Discovery, Research, and InnoVation Economy (MnDRIVE) Initiative through the State of Minnesota. Portions of this study were conducted in the Minnesota Nano Center, which is supported by the National Science Foundation through the National Nano Coordinated Infrastructure Network (NNCI).
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