Lead halide perovskite solar cells (PVSCs) exhibit high efficiencies and are based on abundant materials; further, they can be deposited on flexible substrates using easy fabrication processes. Here, we report a way to fabricate a 1 cm(2) perovskite solar cell outside a glovebox (humidity below 40%) via a modified two-step method with a FTO/TiO2/perovskite/Spiro-OMeTAD/Au structure. This modified two-step method is based on the "dynamic spin-washing method" After dipping the perovskite films into a methylammonium iodide solution, they were washed with isopropyl alcohol (IPA) at different spin speeds. The surface morphology and crystallinity of the perovskite layer were drastically improved using this method. We also investigated and conducted an experiment to explain the effect of the dynamic spin-washing on the surface morphology and crystallinity. Lastly, we optimized the thickness of the TiO2 layer and observed a maximum power conversion efficiency of 13.75% and 11.78% for small- and large-area devices, respectively.