Optical transitions and point defects in F:SnO 2 films: Effect of annealing

•We use AFM and reflectivity measurements to study the surface morphology of FTO films.•We present detailed analysis of optical absorption spectra for spray deposited FTO.•Two optical transitions involving a defect level at Ec −0.61eV have been identified.•Fluorine produces a complex defect acting as a double donor in as-deposited films.