This article discusses printing technologies for OLEDs and examines the ways in which OLEDs are transforming the way we define structure and light.
By Barry Young
Osram, Panasonic, Philips, and Lumiotec announce new OLED lighting products. GE and Fraunhofer pursue roll-to-roll production of OLED lighting panels. Samsung announced the production of a flexible display for 2012. BOE (China) announces plans and Capex to build a sixth Gen Fab in Mongolia. DuPont announces joint development agreement with Korean display maker to use nozzle printing for TVs.
The principle of light from OLEDs was discovered in the 1960s, but it took work by Ching Tang and Steve Van Slyke of Kodak in the late 1980s to make OLEDs function over a reasonable time. They discovered that if the light-emitting material were surrounded by injection and transport layers, the lifetime would increase. Their work to design a stack of organic material in 1987 led to the origin of an industry. There are many stack designs, as shown in Figure 2.
The single-stack design is used for displays, while the multiple-stacked designs are used in lighting and for some TVs. The commercial production of all current OLED display and lighting products use small-molecule material in a powder form that is deposited on a glass substrate under vacuum. VTE is a mature technology that uses a fine metal mask (FMM) for patterning of the RGB sub-pixels for displays and layers of red, green, and blue for deposition. Herein lies the opportunity for printing, because when the light emitting material is deposited using the FMM, the material-utilization rate is 3-5%, and when the other organic material is deposited without the FMM, the material utilization is 20-25%.
Patterning requires that each color have its own source. This is the case for printing, which has been made by a number of companies and scientists:
- Printing has high material utilization in the range of 75-85%.
- Printing enables fine patterning.
- Printing equipment is less expensive than vacuum deposition (VTE).
- Printing is compatible with roll-to-roll manufacturing and very thin substrates (<100 µm).
- Roll-to-roll processes can be expanded at very low capital costs by increasing width of the substrate or by speeding up the roll.
- OLEDs in solution can be printed, and new approaches to organic transistors allow printing.
Printing can be performed at atmosphere and at low temperatures.
Did you enjoy this article? Click here to subscribe to the magazine.