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The degradation of organic light-emitting diodes (OLEDs) is a very complex issue, which might include interfacial charge accumulation, material diffusion, and electrical-induced chemical reaction during the operation. In this study, the origins of improvement in device stability from inserting a hole injection layer (HIL) at the indium tin oxide (ITO) anode are investigated. The results from aging single-layer devices show that leakage current increases in the case of ITO/hole transport layer contact, but this phenomenon can be prevented by inserting molybdenum oxide (MoO3) or 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN6) as an HIL. Moreover, X-ray photoemission spectroscopy suggests that the diffusion of indium atoms and active oxygen species can be impeded by introducing MoO3 or HAT-CN6 as an HIL. These results reveal that the degradation of OLEDs is related to indium and oxygen out-diffusion from the ITO substrates, and that the stability of OLEDs can be improved by impeding this diffusion with HILs. [ABSTRACT FROM AUTHOR]

We demonstrate an alternating current (AC)-driven organic light emitting diodes (OLED) with lithium fluoride (LiF) insulating layers fabricated using simple thermal evaporation. Thermal evaporated LiF provides high stability and excellent capacitance for insulating layers in AC devices. The device requires a relatively low turn-on voltage of 7.1 V with maximum luminance of 87 cd/m² obtained at 10 kHz and 15 Vrms. Ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy are employed simultaneously to examine the electronic band structure of the materials in AC-driven OLED and to elucidate the operating mechanism, optical properties and electrical characteristics. The time-resolved luminance is also used to verify the device performance when driven by AC voltage. [ABSTRACT FROM AUTHOR]

We report the correlation of the electrical properties of the p-doped layer in an interconnection unit with the performance of tandem organic photovoltaic (TOPV) cells where the interconnection unit (ICU) is composed of an electron-transporting layer (ETL)/metal/p-doped hole-transporting layer (p-HTL) by systematically varying the doping concentration of the p-HTL in the ICU. The open circuit voltage is significantly increased as the doping concentration of the p-HTL increases due to the reduction of the difference between the Fermi level and the highest occupied molecular orbital level of the p-HTL. The fill factor is also enhanced with increases in the doping concentration of the p-HTL due to the enhancement of the conductivity in the p-HTL and efficient hole transport at the interface between Ag and the p-HTL through the tunneling process, rather than through the thermionic process. [ABSTRACT FROM AUTHOR]

A perfect ohmic contact is formed at the interface of indium tin oxide (INTO) and N,N'-did(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) using ReO3 as the interfacial layer. The hole injection efficiency is close to 100% at the interface, which is much higher than those for interfacial layers of 1,4,5,8,9,11-hexaazatripheylene hexacarbonitrile (HAT-CN) and MoO3. Interestingly, the ReO3 and MoO3 interfacial layers result in the same hole injection barrier,≈0.4 eV, to NPB, indicating that the Fermi level is pinned to the NPB polaron energy level. However, a significant difference is observed in the generated charge density in the NPB layer near the interfacial layer/NPB interface, indicating that charge generation at the interface plays an important role in forming the ohmic contact [ABSTRACT FROM AUTHOR]

A perfect ohmic contact is formed at the interface of indium tin oxide (INTO) and N,N'-did(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) using ReO3 as the interfacial layer. The hole injection efficiency is close to 100% at the interface, which is much higher than those for interfacial layers of 1,4,5,8,9,11-hexaazatripheylene hexacarbonitrile (HAT-CN) and MoO3. Interestingly, the ReO3 and MoO3 interfacial layers result in the same hole injection barrier,≈0.4 eV, to NPB, indicating that the Fermi level is pinned to the NPB polaron energy level. However, a significant difference is observed in the generated charge density in the NPB layer near the interfacial layer/NPB interface, indicating that charge generation at the interface plays an important role in forming the ohmic contact [ABSTRACT FROM AUTHOR]