In this work post-growth annealing effect on CdSe/SiO 2 thin films grown by rf-magnetron co-sputtering technique was investigated. Annealed samples were characterised by Raman scattering, grazing incidence X-ray diffraction and room temperature photoluminescence. The nanocrystals (NCs) size changed from 1.5 to 5 nm by varying the annealing temperature from 550 to 400 °C. Evaporation of Se at high temperatures was invoked to explain this phenomenon. Fowler–Nordheim tunnelling mechanism was found to be responsible for carrier transport for samples with bigger CdSe NCs sizes, and which showed better photovoltaic properties.