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.
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.
Coronary Heart Disease (CHD) is one of the leading causes of death worldwide, claiming over seven million lives each year. Permanent metal stents, the current standard of care for CHD, inhibit arterial vasomotion and induce serious complications such as late stent thrombosis. Bioresorbable vascular scaffolds (BVSs) made from poly L-lactide (PLLA) overcome these complications by supporting the occluded artery for 3-6 months and then being completely resorbed in 2-3 years, leaving behind a healthy artery. The BVS that recently received clinical approval is, however, relatively thick (~150 µm, approximately twice as thick as metal stents~80 µm). Thinner scaffolds would facilitate implantation and enable treatment of smaller arteries. The key to a thinner scaffold is careful control of the PLLA microstructure during processing to confer greater strength in a thinner profile. However, the rapid time scales of processing (~1 s) defy prediction due to a lack of structural information. Here, we present a custom-designed instrument that connects the strain-field imposed on PLLA during processing to in situ development of microstructure observed using synchrotron X-ray scattering. The connection between deformation, structure and strength enables processing-structure-property relationships to guide the design of thinner yet stronger BVSs.
Highly sensitive alternate current (ac) impedance measurements with variable temperature have been performed to investigate the optical and electrical failure mechanisms during the glass transition phenomena in the archetypal ITO/TPD/Alq3/Al organic light emitting diode (OLED) structure. Since the device degradation is mainly related to the lower glass transition temperature (Tg) of the N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD), this study is focused on the frequency response of thin TPD films approaching the glassy region. The related experimental data are discussed in the framework of the universal dielectric response model. By ac measurements, TPD glass transition temperature is located and temperature regions with different OLED behaviors are evidenced. The relation between the behaviors of TPD frequency response and of the OLED electro-optical response, while the temperature approaches the glass transition region, is discussed.
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