Development of photochromic device with magnetron sputtered titanium dioxide and tungsten trioxide films

A photochromic (PC) device comprising an electrochromic film (WO3) together with a photoactive film (usually, dye sensitized TiO2) coated on glass and a redox electrolyte (e.g., iodide/trliodide together with lithium salt) reduces the optical transmission under solar illumination and bleaches, again, in dark or at low intensity of light. This work reports, for first time, on an application of sputter coated TiO2 and WO3 films for this type of PC devices. The applicability of TiO2 and WO3 films in PC device is individually investigated in dye solar cells and electrochromic cells, respectively. A dye solar cell with 180 nm TiO2 was shown to be sufficient for the charge generation for electrochromic coloration of the WO3. The compatibility of WO3 and redox electrolyte was studied in electrochromic devices by considering their redox potentials. The bleaching of the PC device has to be adjusted by the so called loss current. To address this, a thin catalytic layer of platinum (Pt) is deposited in between the photoactive and electrochromic layers. The optimized PC device exhibits a visual (solar) transmission modulation from 74 (63) down to 30% (20%) in 40 min under 1.5 A.M. illumination, and the bleaching is regained in 45 min in dark.