Improved electrochromic films of NiOx and WOxPy obtained by spray pyrolysis

Electrochromic films of NiOx and WOxPy were produced by the spray pyrolysis technique. The nickel-oxide-based coatings were obtained from both an alcoholic solution of nickel nitrate and aqueous solution of the mixture nickel nitrate/cobalt nitrate. Coatings obtained from alcoholic solutions showed a noticeable contrast of optical transmittance from fully bleached to colored state. X-ray diffraction analysis showed a slight crystallization in NiOx after electrochemical treatment: one diffraction peak for as-deposited films turned to,three diffraction peaks for electrochemical treated samples. Coatings obtained from aqueous solution of mixture nickel nitrate/cobalt nitrate showed an optimized electrochromic behavior at a Ni:Co proportion of 90:10. At this condition an optical contrast of 50% is found. X-ray diffraction showed that these samples comprised a phase mixture of Co3O4 and NiO.WOxPy samples were obtained from polytungsten gel in which H3PO4 was added. We found that for 8.3 at% of P:W, the electrochromism was optimized. Pyrolytic coatings of WOxPy show superior behavior than those of WOx obtained by spray pyrolysis, both in optical contrast and durability. (C) 2000 Elsevier Science B.V. All rights reserved.