OLED Displays Could be Used in Smart Product Packaging

European researchers have developed a cost-effective method for manufacturing flexible displays in much the same way that newspapers are printed. Their work promises to revolutionise packaging, advertising and even clothing.

Ultra-thin and energy efficient displays that use organic compounds to emit light have been stirring up excitement in the consumer electronics industry for several years. Organic Light Emitting Diodes (OLEDs) are already being used commercially in some high-end flat-screen televisions, offering superior image quality, wider viewing angles and lighter power consumption than the current generation of Liquid Crystal Display (LCD) and plasma flat-panel TVs.

But OLEDs' unique properties mean the displays using them can be put to a far wider range of uses, from electronic paper to adaptive clothing - so long as production costs can be brought down.

"Lowering production costs is extremely important if OLED devices are to become more widespread, and particularly if they are not just going to be restricted to high-end applications," explains Arto Maaninen, technical manager of the printed electronics department of the VTT Technical Research Centre in Finland.

Maaninen led the team of researchers behind the EU-funded ROLLED project, which developed a technique for manufacturing OLED devices at considerably lower cost than current methods.

Whereas the OLEDs now making their way into TV sets and some mobile devices are manufactured in a glass substrate, the ROLLED researchers print their OLEDs onto flexible protective films, a procedure known as roll-to-roll processing that allows thousands of devices to be rapidly and cost-effectively produced in a single "print run."

As part of their work, the researchers developed printable nano-particle indium tin oxide (ITO) coatings to form the anode, and they developed a new low-work function metal cathode, with the light-emitting organic layer sandwiched in between.

As an electric current passes from the anode to the cathode layer, the organic compound emits light that, depending on the application, can create a high-contrast TV image or a simple coloured sign. Each OLED sheet is just a fifth of a millimetre thick - equivalent to three or four sheets of paper.

"The biggest cost saving is on equipment. The equipment needed to print OLED displays is widely available, so the initial manufacturing costs are lower compared to other techniques. The material costs are about the same, but you can produce many more units in a much shorter period of time," Maaninen says. "This brings down overall production costs three to five fold."