Hybrid Organic-Inorganic Perovskites are largely investigated worldwide for Photovoltaics[1] today, due to their unique properties. We have previously developed a patented [A. Alberti, E. Smecca, A. La Magna, S. Perugini, M. Abbiati. Method and apparatus for deposition of a layer of perovskite on a substrate. IT20210001898 (granted) - EP4284969 (granted) - US20240117524A1 (filed)] innovative vacuum deposition method called Low-Vacuum Proximity-Space-Effusion (LV-PSE)[2] to prepare CH₃NH₃PbI₃ (MAPbI₃) thin film for semitransparent perovskite solar cells. The method requires lower investment cost for equipment than conventional evaporation and consists of a two-step deposition under low vacuum conditions to produce high-quality thin layers of phase-pure MAPbI_3. They reached an average efficiency of 14.4% with 150 nm-thick active layers in p-i-n devices. An in-depth study of the deposition process and conversion mechanism from PbI₂ to MAPbI₃ has been carried out to further improve the quality of the films. In particular, we investigated how the working pressure and substrate temperature of the first step impact on the quality not only of the PbI₂ film but also of the final MAPbI₃. X-Ray diffraction (XRD) and Spectroscopic Ellipsometry (SE) were used to investigate the structural and optical properties of the deposited films, while the morphology has been studied by Scanning Electron Microscopy. We found that using a working pressure of 2x10^-2 mbar, the prepared PbI₂ films are more oriented along the [001] direction, as attested by the lower full width at half maximum values of the rocking curves. This perovskite structure is also more reproducible than in samples prepared at a pressure of 6x10^-3 mbar, as attested by the narrower spread of the collected data. We suggest that the higher reproducibility at the higher working pressure benefits from the lower deposition rate (~40nm/min) that helps the atoms’ arrangement after they reach the substrate. At the lower pressure, a higher PbI₂ deposition rate (~60nm/min) is achieved. The second step, consisting of methylammonium iodide (MAI) deposition, has been optimized to define the process window for the complete conversion of PbI₂ into MAPbI₃. We found that the MAI deposition time is strictly dependent on the first-step process, currently enabling a net maximum deposition rate for the complete conversion of ~30nm/min. This value is comparable with the highest value reported in literature for MAPbI₃ co-evaporation[3]. As an advantage, our two-step deposition still leaves room for improvement based on deposition pressures and temperature. Device preparation using LV-PSE layers deposited with the two different pressures is ongoing.