Prof. Marumoto clarifies the operating mechanism of light-emitting electrochemical cells, which are less expensive than OLEDs
Light-emitting electrochemical cells (LECs) are one of the organic light-emitting devices. Compared to organic light-emitting diodes (OLEDs), LECs have a simpler structure and are more flexible, and can be manufactured at lower cost by using printing technology. LECs also have the advantage of being able to be driven by lower voltages than OLEDs, and are attracting attention as the next generation of energy-saving light-emitting devices. However, the operating mechanism remains unresolved at the microscopic level, and this has been a barrier to research into its practical application.
In this study, we investigated LECs using super yellow, a typical organic light-emitting material. Using the electron spin resonance (ESR) method, we observed the charge spin state of the LEC while it was operating, and found that both emission and ESR increased as the voltage applied to the LEC was increased. Furthermore, from theoretical analysis of the observed signals, it was determined that the origin of the increase in ESR is the holes and electrons electrochemically doped (injected) into the superyellow. The fact that the doping progression correlates with the increase in luminance suggests that the electrochemically doped charge is distributed on the emission layer as the operating mechanism.
The method developed by this research team provides unprecedented molecular-level information on the operating mechanism of luminescent electrochemical cells. Based on this information, it is expected that product development of low-cost, less environmentally hazardous light-emitting devices can be efficiently advanced.
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