► Synthesis of nanocrystalline ZnO thin films onto glass and ITO coated glass substrates by SPT. ► The substrate temperature dependent properties of ZnO thin films were investigated. ► The sample deposited at 450 °C shows the better photoelectrochemical performance. A simple and inexpensive spray pyrolysis technique (SPT) was employed for the synthesis of nanocrystalline zinc oxide (ZnO) thin films onto soda lime glass and tin doped indium oxide (ITO) coated glass substrates at different substrate temperatures ranging from 300 °C to 500 °C. The synthesized films were polycrystalline, with a (0 0 2) preferential growth along c-axis. SEM micrographs revealed the uniform distribution of spherical grains of about 80–90 nm size. The films were transparent with average visible transmittance of 85% having band gap energy 3.25 eV. All the samples exhibit room temperature photoluminescence (PL). A strong ultraviolet (UV) emission at 398 nm with weak green emission centered at 520 nm confirmed the less defect density in the samples. Moreover, the samples are photoelectrochemically active and exhibit the highest photocurrent of 60 μA, a photovoltage of 280 mV and 0.23 fill factor (FF) for the Zn 450 films in 0.5 M Na 2SO 4 electrolyte, when illuminated under UV light.