Y.-T. Lin, L.-Y Chen, Chung-Chih Wu, K.-T. Wong, R.-T. Chen, Y.-Y. Chien,
Volume 2, Issue 1 (2-2008)
Abstract
In this article, we report the studies of various device architectures of organic lightemitting devices (OLEDs) incorporating highly efficient blue-emitting and ambipolar carriertransport ter(9,9-diarylfluorene)s, and their influences on device characteristics. The device structures investigated include single-layer devices and multilayer heterostructure devices employing the terfluorene as one functional layer. It is found that, although these terfluorenes are capable of bipolar carrier transport, rather poor device performance of single-layer devices in comparison with multilayer devices indicates that the heterostructure is still essential for balancing hole/electron injection and currents, for achieving high emission efficiencies, and for full utilization of high luminescence efficiency of these terfluorenes. With the heterostructure of hole-transport layer/terfluorene/electrontransport layer and careful choice of carriertransport materials, effective hole and electron injection, confinement of carriers, and confinement of excitons in terfluorenes are achieved. As a consequence, a highly efficient (4.1% quantum efficiency), low-voltage (~2.5 V turn-on voltage), and color-saturated nondoped blue-emitting device is demonstrated. Such high electroluminescent efficiency is consistent with high photoluminescent quantum yields of these terfluorenes and is competitive with those of efficient doped blue OLEDs.
Maral Ghoshani, Abbas Behjat, Fatemeh Jafari, Naimeh Torabi,
Volume 7, Issue 1 (6-2013)
Abstract
In this research, the lifetime of green organic light emitting diodes (OLEDs) is studied using four passivation layers. To encapsulate the OLEDs, MgF2, YF3, composed of alternating MgF2/ZnS and YF3/ZnS layers were grown by thermal vacuum deposition. Measurements show that the device lifetime is significantly improved by using YF3 and ZnS as passivation layers. However, diodes encapsulated by MgF2/ZnS and YF3/ZnS nano-structures show a highly efficient gas diffusion barrier that results in a longer lifetime of the devices. The half lifetime of the green OLEDs reached 1200 minutes using YF3/ZnS layers. The electroluminescence (EL) and current-voltage characteristics of the devices were also examined to compare the electrical and the emissivity properties of the devices before and after encapsulation. This simple and inexpensive thin-film encapsulation method would be potentially employed to capsulate top emitting OLEDs and flexible OLEDs due to their good performance and easy fabrication.
