Nanocrystalline Ni ferrite thin film was prepared by electrospray deposition technique and characterized by different analytical techniques at different annealing temperatures. All these films were studied by photovoltaic-assisted water electrolysis system for solar to hydrogen production efficiency measurement. Highly dense and uniform surface morphology was observed in as-deposited film, which changed into agglomerated nanocrystalline grains of irregular size and shape with change in annealing temperature. The X-ray photoelectron spectroscopy study showed that the as-deposited film was a mixture of an oxyhydroxide form of iron and an Ni2O3 form of nickel, whereas it changed into ferrite phase with change in annealing temperature. The as-deposited film was observed to be of amorphous phase, which changed to crystalline cubic spinel structure with change in annealing temperature. The solar to hydrogen production efficiency was found to increase in a film with an increase in annealing temperature. The film annealed at 500 degrees C showed a high solar to hydrogen production efficiency (8.29%) with constant performance of up to initial 500?h. Thereafter, the performance slowly declined by 11% when up to 1000?h. Copyright (c) 2011 John Wiley & Sons, Ltd.