Optical and Electrical Properties of Cobalt Chloride Doped Polyvinylalcohol Polyvinylpyrrolidone Blend.

Films of Cobalt Chloride Doped Polyvinylalcohol - Polyvinylpyrrolidone blend were prepared by solution casting method, in the doping range 0 wt% up to 42 wt%. These films were characterized by XRD, UV-Visible spectrometry, FTIR, thermal analysis and electrical measurements. The films were semi-crystalline, with an average crystallite size of few nanometers. The optical band gap due to indirect allowed transitions (in k-space) decreases from 4.6 eV for 1.5 wt% doping level to 4.0 eV at 35 wt% doping level. In addition, absorption peaks were observed at 2.3 eV, 3.0 eV and 1.7 eV, which indicate that doping results in formation of allowed energy bands within the forbidden gap. The Urbach energy, which measures the width of band tails within the forbidden gap, is found to significantly decrease with increase in doping level. DC electrical measurements show a good fit for 3-D Variable Range Hopping model of conductivity. The temperature variation of electrical resistivity obeys the Arrhenius relation, from which the activation energy obtained is found to decrease from 4.1 eV for 1.5 wt% doping level to 3.1eV for 19 wt% doping level. [ABSTRACT FROM AUTHOR]