The present paper reports for the first time on the fabrication of highly efficient solar cells based on a perovskite layer produced by a sequential deposition method coupling thermal evaporation and slot-die coating. Thermally evaporated PbI₂ films were converted into perovskite by slot-die coating a solution containing the organic MA and FA cations. Careful optimization of the coating parameters resulted in uniform double-cation perovskite films with an optical band gap of 1.64 eV. This work highlights the need for a DMSO (Dimethyl Sulfoxide) vapor treatment performed on the evaporated PbI₂ film to obtain high-quality perovskite layers after the conversion step. Thus, a simple and short pre-treatment has been designed to induce the formation of porous PbI₂(DMSO)_x complex phases enabling a fast and complete perovskite conversion process. Thereby, the champion device delivers a power conversion efficiency of 19.8% with enhanced short-circuit current, open-circuit voltage, and fill factor compared to control devices without treatment.