Method for preparing an electrochromic device

A method for preparing an electrochromic device, comprising:

• inserting monovalent cations into an electrochromic layer comprising a reducing electrochromic material;
• and
• laminating the electrochromic layer and an ion storage layer via an electrolyte layer,
• wherein both the electrochromic layer and the ion storage layer are laminated in a colored state;
• the monovalent cations are inserted into the electrochromic layer by thermal evaporation deposition;
• the thermal evaporation deposition is performed under conditions of a pressure of 10 mTorr or less and a temperature in a range of 500° C. to 700° C.;
• wherein the thermal evaporation deposition is performed so that a separate metal layer composed of a source of monovalent cations is not formed;
• and
• a content of monovalent cations inserted into the electrochromic layer is in a range of 1.0×10−8 mol to 1.0×10−6 mol, wherein the mole number of the monovalent cations inserted into the electrochromic layer is equal to a mole number of electrons present per cm2 of the electrochromic layer which is obtained by dividing a charge quantity (C/cm2) of the electrochromic layer with the Faraday constant (C/mol).