In this paper, we use X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy to investigate the structural and morphological properties of methylammonium lead iodide (MAPbI3) thin films deposited on flat TiO2 substrates, as obtained with and without the use of chlorine precursors. We demonstrate that the presence of Cl precursors assists the growth of oriented MAPbI3 domains along a specific growth direction. Such features are attributed to the proximity of the Cl species to the interface with the TiO2 substrate.