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Researchers from the University of Tsukuba have analyzed the operating mechanism of light-emitting electrochemical cells, which are garnering interest as the future of energy-saving light-emitting devices, by employing the electron spin resonance method. They observed a correlation between the advancement of hole and electron injection into organic light-emitting materials and the increase in luminance. This finding implies that as part of the operation mechanism, the injected charges spread across the light-emitting layer.

Tsukuba, Japan—Light-emitting electrochemical cells (LECs) are a type of organic light-emitting devices. Compared to organic light-emitting diodes (OLEDs), LECs exhibit a simpler structure, greater flexibility, and can be manufactured at lower costs using the printing technology. Moreover, LECs require lower voltages than OLEDs for operation, making them an appealing prospect for the next generation of energy-saving light-emitting devices. Despite their potential, the microscopic-level functioning of these devices remains unclear, impeding research on their practical applications.

Herein, the researchers investigated LECs made from Super Yellow, a commonly used organic light-emitting material. By employing the electron spin resonance (ESR) method, they examined the spin states of the charges within the LECs during operation. They noted that as the voltage applied to the LECs was increased, emission and ESR increased. Further, theoretical analysis of the observed signals led to the conclusion that the increasing ESR originated from holes and electrons being electrochemically doped (injected) into Super Yellow. Interestingly, the correlation between the progress of this doping and the increase in luminance suggests that as part of the device's operation mechanism, these doped charges spread across the light-emitting layer.

The techniques developed by this research team provide unprecedented molecular-level insights into the operation mechanisms of LECs. It is anticipated that these insights can help to effectively drive the development of affordable, environment-friendly light-emitting devices.

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JSPS KAKENHI (Grant Number JP19K21955), Japan; JST PRESTO, Japan; MIKIYA Science and Technology Foundation, Japan; Iketani Science and Technology Foundation, Japan; Iwatani Naoji Foundation, Japan; University of Tsukuba, Pre-Strategic Initiatives 'Development Center for High-Function and High-Performance Organic‒Inorganic Spin Electronics', Japan; JST ALCA (Grant Number JPMJAL1603), and JST MIRAI (Grant Numbers JPMJMI20C5, JPMJMI22C1, and JPMJMI22E2), Japan

Original Paper

Title of original paper:

Investigating the operation mechanism of light-emitting electrochemical cells through operando observations of spin states

Journal:

Communications Materials

DOI:

10.1038/s43246-023-00366-3

Correspondence

Professor MARUMOTO Kazuhiro
Tsukuba Research Center for Energy Materials Science (TREMS) / Institute of Pure and Applied Science, University of Tsukuba

Related Link

Tsukuba Research Center for Energy Materials Science (TREMS)
Institute of Pure and Applied Sciences