OLED with Hole-Transporting Layer Fabricated by Ink-Jet Printing F. Villani, * 1 P. Vacca, 1 R. Miscioscia, 1 G. Nenna, 1 G. Burrasca, 1 T. Fasolino, 1 C. Minarini, 1 D. della Sala 2 Summary: 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 electrolumi- nescent 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. Keywords: electrical and optical properties; hole-transporting layers; ink-jet printing; OLED; polymer Introduction Ink-jet printing (IJP) provides a control- lable method for selectively depositing solution-processed functional materials as thin films within well defined areas with a high degree of accuracy: small amounts of functional materials can be deposited by solution on defined surface areas and with the desired shape. [1–3] Thanks to this technology it is possible to perform mate- rial deposition and patterning at the same time. Moreover, the deposition does not need any employment of expensive masks and patterning does not require any chemical processes as photoresist activation and development, wet etching of undesired structures or other material subtraction- related treatments which can induce defects in functional organic layers. All this issues make this technology attractive for organic light-emitting diodes applications in com- parison with the technologies convention- ally employed in the organic material deposition (thermal evaporation in the case of small organic molecules, and spin-coat- ing in the case of polymer materials). Indeed, IJP technology allows to overcome the traditional techniques limits related to large substrates coverage, solution wastage and lack of lateral patterning capability. [4–6] Thus, IJP assumes a key role in high resolution full-colour display applications thanks also to other remark- able advantages such as the lack of sensitivity to substrate defects being a contactless method, the applicability to several kinds of substrate including the flexible ones, the applicability to almost any Macromol. Symp. 2009, 286, 101–106 DOI: 10.1002/masy.200951213 101 1 Portici ENEA Research Center, Piazzale Enrico Fermi 1, 80055 Portici (NA), Italy Fax: þ39 0817723344; E-mail: villani@portici.enea.it 2 Casaccia ENEA Research Center, Via Anguillarese 301, 00123 S. Maria di Galeria (ROMA), Italy Copyright ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim