Optical and electrical properties of TCNQ doped PMMA films

Abstract

Presently we have prepared TCNQ doped PMMA composite films using Chlorobenzene (CB) as the common solvent. TCNQ is doped at very low concentrations starting from 0.03% to a maximum of 4% and the films are prepared by solution cast method. UV-Visible spectrum is obtained using JASCO UV VIS NIR V 670 Spectrometer which shows absorption by the doped samples in the range 300 nm to 450nm with absorption peak at 400nm. The optical band gaps are calculated using Tauc’s plot, showing a drastic reduction in the band gap of PMMA from about 4.93eV to 2.76 eV, with nearly 50% reduction, such that the composite material enters from non-conducting phase to the conducting phase. The complex impedance analysis is carried out in the frequency range of 40Hz to 5 MHz using Agilent 4294A Precision Impedance Analyzer at room temperature. AC conductivity increases with increase in frequency and also with increase in doping concentrations. Dielectric constant decreases with increase in frequency and attains saturation at higher frequencies. Similar behavior is noticed for dielectric loss also. FTIR investigations done with IR –Prestige-21 FTIR Spectrometer Shimadzu confirmed the additional peak at 2335 cm−1 in the doped samples accounting for the intermolecular charge transfer interaction between the dopant and host matrix. Small shifts in the frequencies are also observed in almost all the bands of the doped samples relative to pure PMMA. The thermal stability of the samples is studied with Universal TA-SDT Q600 indicating that the weight loss is more for doped samples compared to pure film, confirming their thermal stability over the undoped film. We have calculated the Urbach Energy (Eu) of the samples which is about 0.267 eV for pure PMMA and increasing up to 0.471 eV for 4% doped sample. The properties of these transparent and electrically conducting films can be tailored by using the nano particles, dyes, inorganic salts or ionic liquids as the secondary dopants. Films can be used in the construction of transparent electrodes, dielectric films or in other electronic devices.