Real Time Measurements of the State of Charges in OLED Devices

– New technology that can reveal the charging state during a short period before light emissions –

Researchers: Takayuki Miyamae, Senior Researcher, the Nanoscale Interface Characterization Group, the Nanomaterials Research Institute, and Noriyuki Takada, Senior Researcher, the Photo-induced Materials Chemistry Group, the Research Institute for Sustainable Chemistry


The researchers have developed a time-resolved measurement technique for sum frequency generation spectroscopy (SFG spectroscopy). It is capable of non-destructive, real-time measurement of the state of molecules and electric charges inside OLED devices that are emitting light.

Figure 1
Outline of the newly developed time-resolved measurement equipment

Social Background of Research

There has been demand for a technology capable of non-destructive analyses and measurements of information on the charged carriers in the specific organic layers, to make multilayer laminated OLED devices more efficient, save their energy consumption, and extend their useful lifetime. AIST has expanded SFG spectroscopic technique capable of selectively measuring and evaluating information on molecules in the interior interfaces of solids, to develop a technology to measure and evaluate the vibrational spectra of the molecules in individual organic layers in the OLED devices during the light emission.

Technique Developed by the Researchers

Based on previously developed “electric-field induced doubly resonant SFG spectroscopy,” the researchers realized time-resolved measurement by varying the difference between the timing of laser illumination used in SFG spectroscopy and the timing of pulse bias voltage application to an OLED device. Since the organic layers of multilayer OLED devices are only a few tens of nanometers thick, high accuracy and high temporal resolution are required to investigate the charges moving in the organic layers. With the newly developed technique, it is now possible to track the charge carriers in the OLED devices with a precision of several tens of nanoseconds.

Future Plans

The researchers will continuously investigate information inside OLED devices during operation and after extended periods of operation, aiming to clarify the mechanism of charge transfer, extract the factors for improving transport characteristics, and clarify the mechanism of degradation caused by operation.

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