We confirmed that the gas blowing condition during perovskite formation is suitable for fabricating large-scale cells composed of a PEDOT:PSS layer as a scaffold. Gas blowing minimized the defects at the interface between the perovskite and PEDOT:PSS and created a flat perovskite layer. The crystallization process by which the perovskite layer grew was different from one-step spin-coating. Gas blowing led to a perovskite layer with orientation along the (310) plane.