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.

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In this paper, we present a correlation study between the working temperature of OLEDs (Organic Light Emitting Diodes) and the electroluminescence and driving voltage changes. The aim is to investigate the relationship between the operating temperature and the aging mechanisms. We have found that performances degradation of devices is strictly related to the glass transition temperature (Tg) of organic layers, and that electrical failure is reached only for temperatures higher than Tg.

Zinc oxide (ZnO) nanogenerators have attracted increasing interest in the scientific community for use in energy harvesting and mechanical sensing applications. Understanding the interplay between piezoelectricity and semiconductor physics is fundamental to enhancing these devices’ performances, although direct characterization at the nanoscale is challenging. With this work, we present a new strategy to improve piezoresponse force microscopy (PFM) measurements and analysis. This strategy was applied to study the piezoelectric performances of ZnO nanowires grown on seed layers deposited by gravure printing onto flexible substrates. We demonstrate the influence of nanowire diameter and atomic force microscope (AFM) tip position on the piezoresponse amplitude. We also explain our results with simulations showing the importance of considering semiconducting properties in the analysis.

Carbon nanotube (CNT) and polymer composite materials were obtained using two manufacturing processes. The first method is dispersion of CNT in a solvent-doped poly(ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) solution. The composite retains high optical properties because of the polymeric system and shows improved electrical properties. The second method is in situ polymerization of ethylenedioxythiophene (EDOT) in the presence of CNT. This procedure assures a uniform CNT distribution in a highly conductive p-EDOT layer with reduced optical transmittance. The composites were analyzed for optical transmittance, surface energy, polarity, distribution, and resistivity, and then they were used as an anodic layer in organic light-emitting diode (OLED) manufacturing. The device performances were characterized and compared to that of conventional devices with an indium tin oxide anode. p-EDOT composite layers have shown conductivity and optical transmittance suitable to produce an OLED with a 10 cd/A efficiency.