OLED with Hole-Transporting Layer Fabricated by Ink-Jet Printing

We report about the fabrication of organic light-emitting diodes (OLEDs) ink-jet printing a hole-transporting polymer (PF6, poly(9,9-dihexyl-9H-fluorene-2,7-diyl)) on flexible substrate (PET) and performing the other layers through vacuum thermal evaporation. The aim of the work is to employ the ink-jet printing (IJP) technology, familiar as a method for printing on paper, in optoelectronic applications and to determine how the deposition method affects the functional material film properties and hence the ultimate device performances. In this line of work, ink-jet printed polymer films are compared to same spin-coated polymer from the electro-optical point of view: both prepared materials are adopted as HTLs of electroluminescent devices. All manufactured OLEDs are characterized and their behaviours are investigated and analyzed with theoretical models. The results show differences in current density and optical behaviours between the devices fabricated by means of the above mentioned technologies which can be justified in terms of different trap distribution induced by impurity energy levels associated to each process.