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.