OLEDs manufactured without ITO and lithography

Agfa Materials and Holst Centre have developed an OLED tile that eliminates the need for expensive lithography steps, and also eliminates ITO.

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A European research consortium has demonstrated the world’s first large-area, flexible OLED tile that does not require ITO (indium tin oxide) as a transparent electrode and has printed shunting lines.

The group consists of Agfa Materials, part of the Belgian Agfa-Gevaert Group; Philips Research; and Holst Centre, an open-innovation initiative by IMEC (Belgium) and TNO (The Netherlands).

The result, partly funded by the European Union FP7 Fast2Light project, eliminates costly material and lithography process steps. It is, say the participants, a significant improvement towards low-cost, high volume and large-area manufacturing of flexible OLED lighting.

For OLED lighting to become producible at low cost, it is essential to realize a simple system design and compatibility with roll-to-roll processing. To achieve low cost, elimination of transparent conductive oxides -- normally used as the high-conductive and transparent anode layer -- is the preferred way to go.

Until now, ITO was needed as the supporting layer for the PEDOT/PSS* anode layer. Thanks to Agfa's high-conductive transparent polymer Orgacon™, a PEDOT/PSS-based solution with six orders better conductivity than its predecessor, the use of ITO can now be avoided.

Proof is the latest OLED lighting demonstrator of Holst Centre's shared programs: a homogeneous white OLED tile of 12x12 cm2 without the use of ITO.

However, to obtain homogeneous light distribution over large surfaces like this, some kind of additional current distribution is still needed. Even in the presence of ITO, a grid of metallic shunting lines is needed. In conventional designs, ITO, shunting lines, and insulation lines covering the shunting lines are patterned using photolithography steps.

Holst Centre and its partners have succeeded in direct patterned deposition of these shunting lines by inkjet printing, and combining it with PEDOT/PSS without the need for any photolithography steps.

The participants say that, to our knowledge, this is the first time that ITO-free flexible OLEDs are demonstrated in combination with printed shunting lines, which is an important step towards low-cost manufacturing.

The results were obtained thanks to the combined expertise in the Holst Centre program on Flexible Organic Lighting and Signage and in the EU FP7 Fast2Light project. In these programs, Holst Centre researchers collaborate in mixed teams with academics and resident researchers from industrial partners, including Agfa and Philips Research.

* PEDOT = Poly(3,4-ethylenedioxythiophene), PSS = poly(styrenesulfonate)

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