In order to modulate the solar gains of a building, electrochromic windows can be used. To improve their durability, inorganic solid state electrolytes are considered. This work reports on the investigation of tungsten trioxide (WO3) and lithium phosphorous oxynitride (LiPON) used as electrochromic oxide and solid state ion conductor respectively. The impacts of porosity on the optical and the electrochemical properties as well as the determination of ionic conductivity of LiPON are studied. Electro-optical performances were studied by developing an in-situ experimental set-up allowing the measurement of the spectral transmittance during the electrochemical characterizations. The techniques of chrono-amperometry and simultaneous spectrophotometry were used to determine the coloration efficiency as well as the response times for coloration and bleaching of the WO3 films. Electrochemical impedance spectroscopy was performed to investigate the electrochromic and electrolyte materials. The ionic conductivity was measured for LiPON sandwiched in metal-insulator-metal (MIM) cells.