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Understanding the Superior Temperature Stability of Iridium Light-Emitting Electrochemical Cells

Abstract

Single-layer light-emitting electrochemical cells with from ionic transition metal complexes (iTMCs) are relatively simple to construct and have great potential as cost effective emissive devices. Most studies to date have focused on iTMC devices from ruthenium and iridium chromophores. For practical applications, thermal stability is important for environmenal robustness, and little has been said about their relative thermal stabilty. Here, we studied the device performance of iridium and ruthenium ITMCs with temperature to directly compare their stabilities. The thermal onset of radaint flux loss is found to be 67 °C (152 °F) for iridium devices, 45 °C higher than ruthemium iTMCs, a show of its superior thermal stability. We subsequently used temperature-dependent electrochemical impedance spectroscopy, temperature-dependent photoluminescence spectroscopy, time resolved photoluminescence spectroscopy, and photoluminescence quantum yield measurements to understand the physical origin of this substantial temperature stability difference. Prior postulates suggested that films from iridium complexes would yield better thermal stability than those from ruthenium complexes due to details of the orbital energetics. Instead, it is found that this superiority is owed to the details of kinetic effects—the competing kinetics of multiple recombination pathways and the relative rates of radiative to nonradiative processes. Such information guides the design of iTMC emitters for superior light-emitting electrochemical cells.

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Publication details

The article was received on 13 Feb 2017, accepted on 12 May 2017 and first published on 12 May 2017


Article type: Communication
DOI: 10.1039/C7MH00086C
Citation: Mater. Horiz., 2017, Accepted Manuscript
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    Understanding the Superior Temperature Stability of Iridium Light-Emitting Electrochemical Cells

    M. H. Bowler, T. Guo, L. Bastatas, M. D. Moore, A. V. Malko and J. D. Slinker, Mater. Horiz., 2017, Accepted Manuscript , DOI: 10.1039/C7MH00086C

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