Sequential Processing: Crystallization of Ultrasmooth FA1–xMAxPbI3 Perovskite Layers for Highly Efficient and Stable Planar Solar Cells

Planar perovskite solar cells (PSCs) are promising photovoltaic devices accompanied with the obvious advantages of easy fabrication and scalability. To achieve highly efficient and stable PSCs, the morphology control of perovskite crystallization is crucial. Herein, a novel method toward obtaining high‐quality FA1–xMAxPbI3 films by spin coating methylammonium chloride (MACl) and chlorobenzene (CB) in different sequential processes on the top of substrates is proposed. Controlling the nucleation process is beneficial for the formation of a homogeneous nucleus at the nucleation stage, leading to highly ordered seed crystals and an ultrasmooth perovskite film. As determined by photoluminescence and time‐resolved photoluminescence spectroscopy, the defects and the associated charge recombination are notably reduced by the high crystalline quality of perovskite film. Finally, a champion power conversion efficiency (PCE) of 18.57% is achieved and 91% of the initial PCE is retained after 500 h. The devices are stored in an ambient condition with 20% relative humidity (RH) at 30 °C in the dark. Planar perovskite solar cells (PSCs) are promising photovoltaic devices accompanied with the obvious advantages of easy fabrication and scalability. Herein, a method toward obtaining high‐quality FA1–xMAxPbI3 film‐based planar PSCs by sequential deposition of chlorobenzene and methylammonium chloride is proposed. A champion power conversion efficiency (PCE) of 18.57% is achieved and 91% of the initial PCE is maintained after 500 h.