Photoelectrochemical performance of ZnCdSe-sensitized WO3 thin films

Due to its wide gap, WO3 mostly absorbs only the ultraviolet radiation, resulting into lower charge collection and thus necessitating the coupling (doping or sensitization) of WO3 with low band gap materials so as to achieve the photoexcitation and charge separation. This study reports the sensitization of WO3 films with ternary quantum dots (ZnCdSe) using SILAR technique for the first time. The porous WO3 layer was spray deposited using ammonium metatungstate as precursor. The structural, surface morphological and optical properties of the sensitized WO3 thin films were studied. Photoelectrochemical (PEC) studies of the sensitized films showed superior performance to that of unmodified WO3 films. Photocurrent density of 8.53 mA/cm2 (at 0 V vs Ag/AgCl) was observed for film sensitized with 9 cycles of SILAR deposition annealed at 400 °C under nitrogen atmosphere, which is a 120-fold and 14-fold increase in photocurrent density when compared to unsensitized WO3 film and WO3/TiO2 film, respectively. Sensitization with ternary quantum dots as ZnCdSe thus offers two advantages: (i) the lower band gap of ZnCdSe allows it to absorb more energy and in turn produce more charge carriers and (ii) the conduction band of ZnCdSe, which lies above the conduction band of TiO2, results in a better charge transfer from sensitizer to the substrate material.