Inkjet Printed Polymer Layer on Flexible Substrate for OLED Applications

In optoelectronics, inkjet printing (IJP) technology is being developed as an alternative to the traditional techniques for organic materials deposition. In this work, we report the fabrication of organic light-emitting diodes (OLEDs) on the flexible substrate by studying the effect of a surface chemical treatment on the inkjet printed polymer film morphology. The employed piranha treatment increases the substrate surface energy and improves the wettability, thus inducing a decrease in the IJ printed drop thickness. The IJ printed polymer (poly(9,9-dihexyl-9H-fluorene-2,7-diyl)) is the hole-transporting layer (HTL) of a hybrid structure in which the other layers are deposited by vacuum thermal evaporation. Furthermore, in order to determine the effect of the IJ deposition method on the manufactured OLED performances, we compare them to those of devices fabricated using standard technologies. With this aim, OLEDs with the same structure are fabricated by replacing the IJ printed polymer with a spin-coated film employing the same polymer solution. The electrical and optical properties of the electroluminescent devices are investigated and discussed. Despite the lack of thickness uniformity in IJ printed film, which is an intrinsic, technological limit, OLEDs with IJ printed HTL show electro-optical characteristics that are similar to the ones of OLEDs with spin-coated HTL.