 In 1969, S. K. Deb demonstrated electrochromic coloration in WO3 thin films.Deb observed electrochromic color by applying electric field of the order of 104 Vcm−1 across WO3 thin film.In fact, the real birth of the EC technology is usually attributed to S. K. Deb’s seminal paper of 1973, wherein he described the coloration mechanism in WO3.