Observation of interface charge accumulation due to Maxwell-Wagener effect and its impact on the performance of organic devices and molecular deformation

Mitsumasa Iwamoto  

Maxwell-Wagener effect accounts for charge accumulation at the interface between materials, and this fact is well utilized to analyze device characteristics, e.g., I-V characteristics. However the observation of charge accumulation is necessary to deeply understand the charge accumulation phenomena and to further develop the theory of carrier transport in organic device. In this presentation, first I briefly talk about the Maxwell-Wagner effect, and show how the transfer characteristics of organic field effect transistors devices is analyzed using a Maxwell-Wagner model. Then I will show that electric field optical second harmonic generation (EFISHG) measurement is available to directly observe charge accumulation phenomena at the device interface. As examples, carrier behaviors in pemtacene field effect transistors, organic light emit diodes (OLED), and organic memory devices are visualized. In this talk, particular attention is the behavior of charge carriers at the organic memory elements using PVDF. According to the turn-over of PVDF molecules in films, the charge behavior in organic memory devices is analyzed using EFISHG and charge modulation spectroscopy.  As an extension of the Maxwell-Wagener effect, vesicle deformation in solutions under the a.c. field is analyzed, and the effect of charge accumulation is discussed. Also the experiment to probe charge accumulation at the interface between sphere vesicles and solutions is also demonstrated, and I will show the experimental evidence of charge accumulation at the interface by EFISHG.