24.3: Invited Paper: Printed Electrodes for All‐Solution‐Processed Inverted‐Structure OLEDs

A key enabling technology for all‐printed organic light‐emitting diodes is printing electrodes that can be used for anodes or cathodes for conventional or inverted device structures. In both device structures, the first bottom electrodes, which are either transparent or opaque depending on the device structure, are typically printed while the last top electrodes have been deposited by using a vacuum‐based evaporation process because when the last top electrodes are fabricated by using a solution‐based process, under organic layers are easily damaged during the fabrication process. Although so‐called transfer printing process has been often reported for organic devices such as organic solar cells, it has been rarely applied for OLEDs. In addition, no fine patterning has been adopted in such printing processes. As part of our efforts towards all‐printed OLEDs, inkjet‐printed and/or transfer‐printed, finely‐patterned PEDOT:PSS electrodes have been investigated in our lab and most recent achievement will be reported in detail. In order to implement all‐solution‐processed OLEDs, we also studied the inverted‐structure OLEDs, which showed comparable results to the conventional structure OLEDs with the vacuum‐based deposited electrodes.