Efficient electroluminescent devices based on a chelated osmium(II) complex

Efficient devices with air-stable electrodes were fabricated from [Os(bpy)2L]2+(PF6-)2. The resulting devices exhibit red-orange emission with a peak radiance that exceeded 6000 cd m-2 at only 6 V. External efficiencies that were of the order of 1% were achieved. A characteristic turn-on time indicated the importance of ionic space charge effects in the mechanism of device operation

Observation of electroluminescence and photovoltaic response in ionic junctions

Electronic devices primarily use electronic rather than ionic charge carriers. Using soft-contact lamination, we fabricated ionic junctions between two organic semiconductors with mobile anions and cations, respectively. Mobile ionic charge was successfully deployed to control the direction of electronic current flow in semiconductor devices. As a result, these devices showed electroluminescence under forward bias and a photovoltage upon illumination with visible light. Thus, ionic charge carriers can enhance the performance of existing electronic devices, as well as enable new functionalities

A light-emitting memristor

A light-emitting memristor (LEM) is reported based on a metal/mixed conductor/metal structure, where the mixed conductor is the ionic transition metal complex ruthenium(II) tris(bipyridine) with hexafluorophosphate counter ions. The device shows memory effects upon the application of an ac bias, in both current and electroluminescence intensity. The observation of memory in light emission offers the potential for optical read-out of the state of memristive devices. © 2009 Elsevier B.V. All rights reserved

Cascaded light-emitting devices based on a ruthenium complex

The architecture for the fabrication of cascaded light-emitting devices, which was based on a transition metal complex, was analyzed. The patterning of the organic layer of the device was not required by the architecture. In this device, the metal electrode which acted as an anode for one device and a cathode for the neighbouring device. The devices were panelled in a single row on a indium tin oxide (ITO) covered glass. It was observed that architecture allowed the monolithic fabrication of panels, which showed intrinsic fault tolerance to short circuits and were amenble to scaling to large areas

Solid-state electroluminescent devices based on transition metal complexes

Transition metal complexes have emerged as promising candidates for applications in solid-state electroluminescent devices. These materials serve as multifunctional chromophores, into which electrons and holes can be injected, migrate and recombine to produce light emission. Their device characteristics are dominated by the presence of mobile ions that redistribute under an applied field and assist charge injection. As a result, an efficiency of 10 lm/W—among the highest efficiencies reported in a single layer electroluminescent device—was recently demonstrated. In this article we review the history of electroluminescence in transition metal complexes and discuss the issues that need to be addressed for these materials to succeed in display and lighting applications. © 2003 The Royal Society of Chemistry

Electroluminescence in ruthenium(II) dendrimers

We have investigated the electroluminescent properties of polyamidoamine dendrimers containing pendant [Ru(bpy)3]+2 chromophores. Devices were made using indium tin oxide (ITO) and gold electrodes, and they were compared to devices made from [Ru(bpy)3]+2 films. The turn-on time, steady-state current, and electroluminescence efficiency were analyzed in order to provide information about the ionic and electronic carrier mobilities and the degree of self-quenching of luminescence in these materials

Temperature dependence of tris(2,2′-bipyridine) ruthenium (II) device characteristics

The temperature dependence of the current, radiance and efficiency from electroluminescent (EL) devices based on [Ru(bpy) 3] 2+(PF -6) 2 was investigated. It was found that the current increased monotonically with temperature from 200-380 K whereas the radiance reached a maximum near T room. It was analyzed that the quenching of the Photoluninescence (PL) with temperature could be accounted for by the thermal activation to a nonradiative d-d transition. It was also observed that the temperature dependence showed a complex behavior in which transport appeared to be thermally activated with distinct low-temperature and high-temperature characteristics

Addition of a phosphorescent dopant in electroluminescent devices from ionic transition metal complexes

Ionic transition metal complexes have emerged as promising candidates for applications in solid-state electroluminescent devices. This is due to the fact that a single, solution-processable layer sandwiched between two air-stable electrodes can yield high-efficiency devices. In this paper we demonstrate tuning of the emission of these devices in the red part of the spectrum by dispersing an ionic osmium complex into an ionic ruthenium complex matrix. This is shown to lead to devices that are more efficient than those from pristine films of the matrix or the dopant alone. These devices also show improved stability compared to devices based on the matrix and feature an emission spectrum that can be tuned by the concentration of the dopant. © 2005 American Chemical Society

Electroluminescence in ruthenium(II) complexes

We have investigated the electrochemical, spectroscopic, and electroluminescent properties of a family of diimine complexes of Ru featuring various aliphatic side chains as well as a more extended π-conjugated system. The performance of solid-state electroluminescent devices fabricated from these complexes using indium tin oxide (ITO) and gold contacts appears to be dominated by ionic space charge effects. Their electroluminescence efficiency was limited by the photoluminescence efficiency of the Ru films and not by charge injection from the contacts. The incorporation of di-tert-butyl side chains on the dipyridyl ligand was found to be the most beneficial substitution in terms of reducing self-quenching of luminescence

Electroluminescent devices from ionic transition metal complexes

Ionic transition metal complexes (iTMCs) are receiving increased attention as materials capable of yielding efficient electroluminescent devices with air-stable electrodes. The operational characteristics of these devices are dominated by the presence of mobile ions that redistribute under an applied bias and assist in electronic charge injection. This article reviews recent efforts in the field of iTMC devices: i) to understand their physics, ii) to improve their efficiency, colour, turn-on time and lifetime, and iii) to expose their potential applications. © The Royal Society of Chemistry