In-situ investigation of organic devices by using infrared spectroscopy and photoelectron analysis

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In this study, we have investigated organic devices by combing spectroscopic methods and electric measurement. As the former, infrared reflection absorption spectroscopy in the multiple reflection geometry (MIR-IRAS) and photoelelctron yield spectroscopy (PYS) were applied, and as the latter, displacement current measurement (DCM) was used.We have applied DCM technique to various organic devices such as organic transistor, organic electroluminescent devices, and organic bistable devices. Then we found that this technique can give us useful information about the behavior of carrier in organic devices such as carrier injection, accumulation, amount of traps, and spatial distribution of accumulated charge. Concerning organic transisotr, we found that impurity doping to organic semiconductor is enhanced by visible light illumination and proposed a new doping method of "photoinduced doping". MIR-IRAS measurement of pentacene and polythiophene film revealed that the mechanism of the photoinduced doping is the acceleration of charge transfer between host organic semiconductor and guest impurity dopant through photoinduced charge transfer.We developed an apparatus with which photoelectron yield spectroscopy can be measured both in vacuum and atmospheric conditions. Due to purging the inside of a UV monochromatic light source by nitrogen, a wide range of photon energy (4-9eV) is available to cover most organic materials. We also demonstrated that PYS technique can be used to analyze electronic structures of organic/metal interface. Under our advice, very recently, a commercial apparatus for measuring ionization potential of OLED materials have been developed by a Japanese company.