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Enhancement of electrical conductivity of plasma polymerized fluorene-type thin film under iodine and chlorine dopants

Electrical and optical properties of plasma-polymerized fluorene-type (C13H10) iodine-and chlorine-doped thin films are investigated. Fluorene-type thin films are produced using a mixture of biphenyl (C12H10) and methane (CH4) inside a single capacitively coupled radio frequency plasma system. The dopants are mixed with the plasmadirectly as vapor during the deposition. The chemical structures of the generated functional compounds, evaluated by a Fourier transform infrared spectroscopy, exhibit a changeable extension conjugation providing high crosslinking and branching. The structural orders of the doped films are analyzed using X-ray diffraction measurements. The film thickness is measured by ellipsometry. Measured difference in thickness due to doping varies from 16 nm to 50 nm. The structural characterization shows that the doped films are stable and of high quality. The current-voltage characteristics of devices are obtained using two-point probe measurements. As a result of doping, electrical conductivity as high as two orders of magnitude compared to that of the undoped films is measured. In addition, ultraviolet-visible spectroscopy is used to characterize the optical properties. Optical energy band gaps of the doped films as low as 2.4 eV are obtained. In conclusion, plasma processing is proven to improve the optical and electrical properties of the doped films. (C) 2017 Elsevier B.V. All rights reserved.