Photoelectric Cells of Merocyanine Langmuir-Blodgett Films Utilizing Surface Plasmon Excitations
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Photoelectric Cells of Merocyanine Langmuir-Blodgett Films Utilizing Surface Plasmon Excitations Keizo Kato, Futoshi Takahashi, Kazunari Shinbo1, Futao Kaneko1 and Takashi Wakamatsu2 Graduate School of Science and Technology, Niigata University, Ikarashi 2-8050, Niigata 950-2181, JAPAN 1 Department of Electrical and Electronic Engineering, Niigata University, Ikarashi 2-8050, Niigata 950-2181, JAPAN 2 Department of Electrical Engineering, Ibaraki National College of Technology, 866 Nakane, Hitachinaka 312-8508, JAPAN ABSTRACT Short-circuit photocurrents (ISC) due to surface plasmon (SP) excitations have been investigated for the photoelectric cells using Langmuir-Blodgett (LB) films of merocyanine (MC) dye. The MC dye exhibits p-type conduction, and the Schottky and Ohmic contacts are obtained at the interfaces between MC LB films and Al thin films and between MC LB films and Ag thin films, respectively. Since the Schottky diodes show the photoelectric effects, the Schottky photoelectric cells have been constructed. The cells with two kinds of structures, that is, prism/Al/MC/Ag (type I) and prism/MgF2/Al/MC/Ag (type II), have been prepared. In the attenuated total reflection (ATR) method, the types I and II have the Kretschmann and both the Kretschmann and Otto configurations, respectively. SP has been resonantly excited at the interface between Ag and air for the type I and at the interfaces between MgF2 and Al between Ag and air for the type II. The ATR and the ISC properties have been simultaneously measured as a function of the incident angles of the laser beams. The peaks of the ISC have corresponded to the resonant angles of the ATR curves. The electric fields and optical absorptions in the cells have been also calculated using the dielectric constants and the film thicknesses obtained from the ATR measurements. The calculated absorptions in the MC layers as a function of the incident angles have corresponded to the results of ISC. It has been estimated that the ISC for both types I and II could be enhanced by the excitations of SP in the ATR configurations. INTRODUCTION Organic thin films have been attracting a lot of attention for their variety of functions, such as gas sensing, nonliner optics, luminescence, photoelectric effect and so on and various studies have been carried out so far [1,2]. Several studies of the organic photoelectric devices have been reported [3-5]. For the conventional photoelectric devices, high efficiency has not been obtained because of light transmission through organic thin layers, light reflection at the electrodes in the cells and so on. In the ATR configuration utilizing the SP excitation [6-11], strong optical absorption is expected for organic dye ultrathin films in photoelectric cells [12,13]. For the development of photoelectric devices with high efficiency, it is important to evaluate structure, optical and electrical properties of the devices. The ATR properties are measured as a function of the incident angle at a constant wavelength, utilizing the SP resonantly excite
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