Temperature Effect of Ionic Transition Metal Complex Light-Emitting Electrochemical Cells
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Temperature Effect of Ionic Transition Metal Complex Light-Emitting Electrochemical Cells Takeo Akatsuka1,2, Stephan van Reenen3, Enrico Bandiello1, Henk J. Bolink1 1 Instituto de Ciencia Molecular, Universidad de Valencia, C/ Catedrático J. Beltrán 2, ES-46980 Paterna (Valencia), Spain 2 Advanced Materials Research Center, Nippon Shokubai Co. Ltd., 5-8 Nishi Otabi-cho, Suita, 564-8512 Osaka, Japan 3 Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands ABSTRACT Light-Emitting Electrochemical Cells (LECs) consist of solution processable ionic lightemitting materials and use air stable electrodes. Their operational mechanism relies on both ionic and electronic conduction. The dynamic behavior is primarily determined by the ionic conductivity. Here, we demonstrate that with increasing temperature the LECs turn-on faster yet without decreasing the efficiency. This is due to the activation energy of ionic transport and the temperature independent photoluminescence quantum yields. INTRODUCTION Due to great improvement of stability and efficiency of electroluminescent molecular devices in the past few decades [1], a lot of organic light emitting devices have already commercialized into the market. One of the most successful devices among them is the Organic Light Emitting Diode (OLED) [2]. Although OLEDs are used as displays, there is still room for improvement. Especially for application in light source significant improvements are needed to allow a cost compatible with that market. This requires alternative solutions for their design and preparation. For one the air-sensitivity of the electrode injection layer or metal contact use leads to demanding encapsulation protocols [3]. Secondly, the best performing OLEDs consist of a multi-layer stack and are prepared using costly vacuum sublimation techniques [4]. On the other hand, light-emitting electrochemical cells (LECs) which consist of solution processable ionic light-emitting materials and air stable electrodes have the potential to become a cost-efficient light source. When operated using a constant voltage, LECs show changes in their current density, luminance, and efficacy during operation. Recently it has been revealed using both experimental and simulation technique that these phenomena are derived from the ionic movement inside the active layer [5-7]. Since the ionic movement depends on the temperature, LECs performances are strongly temperature dependent. This has implications for their applications, but is also very interesting from a scientific point of view. A few previous researches have appeared where this effect has been studied [8-10]. This proceeding focuses on the temperature effect of LECs employing a series of ionic iridium transition metal complexes (Ir-iTMCs) LECs.
EXPERIMENT The Ir-iTMC LECs were made as follows. The emitting complex, [Ir(ppy)2(bpy)]+[PF6]‐ (1) (where ppy is 2-phenylpyridinato and bpy is 2,2’-bipyridine), [Ir(ppy)2(pbpy)]+[PF6]‐ (2) (where pbpy is 6-phenyl-2,2’-bipyri
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