All-inorganic cesium lead triiodide (CsPbI3) perovskites show high potential for photovoltaic applications due to their excellent thermal stability and suitable bandgap (Eg≈1,72 eV) ideal for tandem device. However, the photovoltaic performances of CsPbI3 perovskite solar cells (PSCs) are significantly restricted by a scarcely controllable crystal quality leading to high nonradiative recombination processes [1]. Therefore, the potential of CsPbI3 is overshadowed by the black-phases (α, β, and γ) structural instability, prone to spontaneous evolution into the photoinactive δ-phase at room temperature. This transition can be accelerated by ambient moisture, resulting in diminished PCE. Consequently, stabilizing black CsPbI3 at room temperature has become a critical topic. The regulation of the nucleation and growth rates has been identified as an efficient strategy for enhanced film coverage [2]. CsPbI3 perovskite films are produced via a cost-effective and straightforward solution-based manufacturing process. However, the nucleation and growth processes are largely uncontrollable, leading to inevitable defects stemming from conventional coating methods. Understanding the fundamental mechanism underlying film formation, specifically in terms of nucleation and growth, is crucial. Identifying this mechanism is a necessary step for precisely adjusting film crystallization kinetics. The optimization of additive engineering has proven to be a successful and straightforward approach in developing Cs-based photovoltaic devices with enhanced efficiency and stability. Consequently, it has emerged as a significant focus in PSC (perovskite solar cell) research. The aim of this work is to obtain a stable CsPbI3 polycrystalline thin film modulating the different parameters involved in the solution processing of the films, spanning from the employed solvent to the use of additives modifying the solution chemistry, to the use of alternative Pb sources DMAPbI3 [3]. The chemistry involving additives currently revolves around the utilization of HI and DMAI [4,5] within the precursors salts solution. Experimental evidence in both scenarios substantiates the formation of the intermediate DMAPbI3 within the solution, HI reacts with DMF and DMAI with PbI2. By synthesizing DMAPbI3 through hydrolysis and utilizing it directly as a lead source in the solution, it's possible to achieve better stoichiometric control involving DMA+ and to produce higher-quality films.The formation of intermediate complexes during the crystallization process assumes a pivotal role. For instance, the inclusion of additives, such as Cl− ions in the precursor solution has a positive impact on the nucleation of perovskites. Importantly, these Cl− ions aid in the nucleation process without becoming part of the perovskite lattice structure itself. This, in turn, leads to the production of perovskite films with enhanced optoelectronic properties, suggesting an improvement in their ability to interact with and respond to light. The presented strategies allow to investigate the effect on the nucleation process and how the existence of solute–solvent crystalline intermediate phases have an impact on chemical reaction kinetics. Finally, the optimized films have been integrated and tested in solar cells.