As the efficiency of perovskite solar cells (PSCs) reached more than 22%, the large-area fabrication of PSCs became another issue receiving growing attention. For large-area PSCs, more reproducibility is required to precisely control the crystallization behavior of perovskites. A two-step process has been preferred to apply large-area coatings of perovskite because of its better reproducibility, but the process has suffered from slow and incomplete conversion of PbI2 to perovskite. In this paper, we propose a fast, simple, two-step methodmediator extraction treatment (MET)for the preparation of a high-quality perovskite film. In MET, a pre-deposited PbI2-DMSO complex film is converted into a peculiar PbI2 film with a porous morphology and unusual crystallographic orientation via the removal of DMSO. PbI2 could be completely converted into MAPbI(3) by a fast reaction with MAI molecules. We demonstrate that this MET process in MAPbI(3)-based PSCs can achieve 18.8% of the maximum power conversion efficiency (PCE) using spin-coating, and 18.3% of the maximum PCE using slot-die coating with a uniform distribution in a 10 x10 cm(2) substrate at a laboratory scale. Moreover, over 18% of PCE could be achieved in only 100 s, and with room-temperature processing.