Optical and electrical properties of cobalt chloride doped polyvinyl alcohol polyvinylpyrrolidone blend

Films of cobalt chloride doped polyvinyl alc. - polyvinylpyrrolidone blend were prepd. by soln. casting method, in the doping range 0 wt​% up to 42 wt​%. These films were characterized by XRD, UV-​Visible spectrometry, FTIR, thermal anal. and elec. measurements. The films were semi-​cryst., with an av. 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 addn., absorption peaks were obsd. 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 elec. measurements show a good fit for 3-​D Variable Range Hopping model of cond. The temp. variation of elec. 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 3.1 eV for 19 wt​% doping level. (c) 2014 American Institute of Physics