Novel Light-Emitting Electrochemical Transistor Using Ruthenium Complex

Abstract

Recently, organic light-emitting transistors (OLETs) which combined organic light-emitting diodes (OLEDs) with organic thin film transistors (OTFTs) have being intensively investigated for application to display. They can control light emission by the gate voltage. So far, we have investigated light-emitting electrochemical cells (LECs) and electrochemical transistors (ECTs) independently. LECs have some advantages about a simple device structure and usage of air-stable metal cathode compared to OLEDs. ECTs also have unique features for lower driving gate voltage than that of OTFTs because the electrochemical doping becomes easier for the formation of the electric double layer in the ECTs. Therefore, a novel concept for the light-emitting electrochemical transistor (LECT) which consists of the light-emitting electrochemical cell (LEC) and the electrochemical transistor (ECT) was introduced. To aim at constructing LECT, four-electrode electrochemical system using interdigitated array (IDA) electrodes was employed to demonstrate the concept of LECT in solution. Cyclic voltammetric (CV) measurement was carried out in acetonitrile solution containing Ru(bpy)3(PF6)2 as redox species and a chemiluminescent material. We confirmed that the light emission was controlled at the electrode potential difference between both fingers of IDA electrodes as source and drain electrodes of the transistor and reference/counter electrodes as gate electrode. The light emission was observed at the electrogenerated chemiluminescent condition where the excited state Ru(II) was produced on the gap distance by the electron exchange reaction of Ru(I) and Ru(III) produced at both fingers of IDA electrodes, respectively. If the electrode potential would be shifted to anodic or cathodic directions, whether Ru(I) or Ru(III) would be not produced, the light emission disappear even at the same bias voltage between the source and drain electrodes (VDS) where the light emission is possible. If VDS is not enough to produce Ru(I) and Ru(III), the light emission does not occur. If VDS is enough to produce Ru(I) and Ru(III) in the diffusion limited condition, the light emission becomes steady state intensity. Therefore, we demonstrated that the light emission can be controlled by VDS and the gate electrode potential in the LECT. We also confirmed that current behavior flowed between source and drain electrodes shows bipolar transistor characteristics. We are now trying to solidify the LECT system in solution to realize LECT device.