The main objectives of the project are to study the effects of the induced strain gradient through compositional graded doping and different substrate orientations in Y-doped BFO and KBiFe2O5 on the optical and electrical properties as well as on the photocatalytic water splitting for hydrogen generation behaviour. The engineering of complex thin film films by inducing controlled structural deformation to allow for the improvement of existing functional properties and the induction of some new ones, is part of the research line promoted by the project director in previous works and scientific projects. The use of controlled structural deformation will allow the optical and electrical properties of thin films to be modified, with the consequence of increasing the efficiency of these materials in applications such as energy generation through water splitting. This research line - increasing the functional performance of thin films in a single experimental stage of production, in a field dominated by volumetric materials - has the potential to make a significant contribution to the advancement of knowledge in the field.