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 alco holic 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 color ed state. X-ray diffraction analysis showed a slight crystallization in NiO x after electrochemical treatment: one diffraction peak for as-deposited fi lms turned to,three diffraction peaks for electrochemical treated samples. Coatings obtained from aqueous solution of mixture nickel nitrate/cobalt ni trate 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 diffrac tion showed that these samples comprised a phase mixture of Co3O4 and NiO.W OxPy 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. Pyroly tic 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.