Fabrication of WO₃ electrochromic devices using electro-exploding wire techniques and spray coating

Electrochromic devices (ECDs) play an important role in smart window applications for blocking heat from sunlight. Tungsten trioxide (WO₃) is one of the best candidates for making electrochromic films. Current manufacturing processes are, however, costly, have long processing time, and often use non-eco-friendly precursors. Here an alternative facile method integrating electro-exploding wire and spray coating techniques is demonstrated for applications in large size ECDs. The electro-exploding wire technique is used to synthesize WO₃ nanomaterials (NMs) in deionized water. The varied size distribution of WO₃ NMs is achieved by changing the exploding voltage. The NMs are characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The exploding voltage of 36 V is selected to generate WO₃ NMs in a wide size distribution for making porous WO₃ films. Subsequently, spray coating is used to disperse WO₃ NM suspension on the ITO/glass substrate to form an electrochromic film. The films are characterized by scanning electron microscopy (SEM) and by cycle voltammetry, chronoamperometry, and chronocoulometry measurements in dilute sulfuric acid. The WO₃ NM films prepared at a high exploding voltage and a high substrate temperature present a higher electrochemical stability. Considering porosity and electrochemical stability, WO₃ NMs exploded at 36 V are used to prepare WO₃ films on substrates heated at 300 °C. The electrochromic WO₃ film can be operated for over 1000 cycles. We demonstrate an ECD with an area of 15 × 15 cm² and propose a way to make large size ECDs with low cost and eco-friendly processes.