Preparation of mixed oxide MoO 3–WO 3 thin films by spray pyrolysis technique and their characterisation

Abstract

Mixed oxide MoO 3–WO 3 thin films have been deposited onto the amorphous and fluorine doped tin oxide (FTO) coated glass substrates at 300°C by using a simple and inexpensive spray pyrolysis technique. Equimolar ammonium tungstate and ammonium molybdate solutions were mixed together in volume proportions and used as precursors for spraying. The samples were annealed at 400°C for 1 h. They were approximately 0.6 μm thick. The structural, electrical and optical properties were studied and values of room temperature electrical resistivity, its activation energy and band gap energy were estimated. The crystallinity of the samples improved with increase in Mo content in the samples. The sample with 2% Mo-oxide in the W-oxide sample exhibited more pronounced electrochromism than other samples including WO 3. The existence of two peaks in the cyclic voltammogram, unlike WO 3, suggests that there are two kinds of oxidation states corresponding to WO 3 and MoO 3. The response times were also improved when Mo oxide is added into the WO 3. The stability of these samples were tested by repeating colour/bleach cycles several times in H 2SO 4 electrolyte.