Some recent studies mainly addressing the preparation and the modification of nanostructured thin films based on WO₃ and their application to photoelectrolysis of aqueous electrolytes are reviewed with the aim of rationalizing the main factors at the basis of an efficient photoanodic response. WO₃ represents one of the few materials which can achieve efficient water photo-oxidation under visible illumination, stably operating under strongly oxidizing conditions; thus the discussion of the structure-related photoelectrochemical properties of WO₃ thin films and their optimization for achieving almost quantitative photon to electron conversion constitutes the core of this contribution.

Dye-sensitized solar cells (DSSCs) were assembled by using the bougainvillea flowers, red turnip and the purple wild Sicilian prickly pear fruit juice extracts as natural sensitizers of TiO₂ films. The yellow orange indicaxanthin and the red purple betacyanins are the main components in the cocktail of natural dyes obtained from these natural products. The best overall solar energy conversion efficiency of 1.7% was obtained, under AM 1.5 irradiation, with the red turnip extract, that showed a remarkable current density (Jsc = 9.5 mA/cm²) and a high IPCE value (65% at λ = 470 nm). Also the purple extract of the wild Sicilian prickly pear fruit showed interesting performances, with a Jsc of 9.4 mA/cm², corresponding to a solar to electrical power conversion of 1.26%.

Charge transfer dynamics in WO₃ photoelectrodes: hydroxyl radicals are the primary water oxidation intermediates generated via valence band hole injection.